diff --git a/backend/src/db/migrations/018_market_comments.sql b/backend/src/db/migrations/018_market_comments.sql
new file mode 100644
index 00000000..3d806246
--- /dev/null
+++ b/backend/src/db/migrations/018_market_comments.sql
@@ -0,0 +1,19 @@
+-- Migration: create market_comments table and thumbs-up deduplication table
+CREATE TABLE IF NOT EXISTS market_comments (
+  id SERIAL PRIMARY KEY,
+  market_id INT REFERENCES markets(id) ON DELETE CASCADE,
+  wallet_address TEXT NOT NULL,
+  content VARCHAR(500) NOT NULL,
+  thumbs_up_count INT NOT NULL DEFAULT 0,
+  is_hidden BOOLEAN NOT NULL DEFAULT FALSE,
+  created_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_market_comments_market_id ON market_comments(market_id, is_hidden, created_at DESC);
+
+CREATE TABLE IF NOT EXISTS comment_thumbs_up (
+  comment_id INT REFERENCES market_comments(id) ON DELETE CASCADE,
+  wallet_address TEXT NOT NULL,
+  created_at TIMESTAMPTZ DEFAULT NOW(),
+  PRIMARY KEY (comment_id, wallet_address)
+);
diff --git a/backend/src/index.js b/backend/src/index.js
index 29f73c59..43391f47 100644
--- a/backend/src/index.js
+++ b/backend/src/index.js
@@ -98,6 +98,8 @@ app.use("/api", appCheckMiddleware);
 // Routes (MERGED — keep ALL)
 app.use("/api/auth", require("./routes/auth"));
 app.use("/api/markets", require("./routes/markets"));
+app.use("/api/markets/:id/comments", require("./routes/comments"));
+app.use("/api/comments", require("./routes/commentActions"));
 app.use("/api/bets", require("./routes/bets"));
 app.use("/api/notifications", require("./routes/notifications"));
 app.use("/api/reserves", require("./routes/reserves"));
diff --git a/backend/src/routes/commentActions.js b/backend/src/routes/commentActions.js
new file mode 100644
index 00000000..70a095ca
--- /dev/null
+++ b/backend/src/routes/commentActions.js
@@ -0,0 +1,69 @@
+"use strict";
+
+const express = require("express");
+const router = express.Router();
+const db = require("../db");
+const logger = require("../utils/logger");
+const jwtAuth = require("../middleware/jwtAuth");
+
+// POST /api/comments/:id/thumbs-up  (JWT required, one per wallet)
+router.post("/:id/thumbs-up", jwtAuth, async (req, res) => {
+  const commentId = parseInt(req.params.id, 10);
+  const walletAddress = req.admin?.sub || req.admin?.wallet_address;
+
+  try {
+    // Insert deduplication record — PK constraint prevents duplicates
+    await db.query("INSERT INTO comment_thumbs_up (comment_id, wallet_address) VALUES ($1, $2)", [
+      commentId,
+      walletAddress,
+    ]);
+
+    const { rows } = await db.query(
+      "UPDATE market_comments SET thumbs_up_count = thumbs_up_count + 1 WHERE id = $1 RETURNING thumbs_up_count",
+      [commentId]
+    );
+
+    if (rows.length === 0) {
+      return res.status(404).json({ error: "Comment not found" });
+    }
+
+    res.json({ thumbs_up_count: rows[0].thumbs_up_count });
+  } catch (err) {
+    if (err.code === "23505") {
+      return res.status(409).json({ error: "Already thumbed up" });
+    }
+    if (err.code === "23503") {
+      return res.status(404).json({ error: "Comment not found" });
+    }
+    logger.error({ err: err.message, commentId }, "Failed to thumbs-up comment");
+    res.status(500).json({ error: "Internal server error" });
+  }
+});
+
+// DELETE /api/comments/:id  (admin JWT required — sets is_hidden = TRUE)
+router.delete("/:id", jwtAuth, async (req, res) => {
+  const commentId = parseInt(req.params.id, 10);
+
+  // Require admin role
+  if (!req.admin?.isAdmin) {
+    return res.status(403).json({ error: "Admin access required" });
+  }
+
+  try {
+    const { rows } = await db.query(
+      "UPDATE market_comments SET is_hidden = TRUE WHERE id = $1 RETURNING id",
+      [commentId]
+    );
+
+    if (rows.length === 0) {
+      return res.status(404).json({ error: "Comment not found" });
+    }
+
+    res.json({ success: true });
+  } catch (err) {
+    logger.error({ err: err.message, commentId }, "Failed to hide comment");
+    res.status(500).json({ error: "Internal server error" });
+  }
+});
+
+module.exports = router;
diff --git a/backend/src/tests/comments.test.js b/backend/src/tests/comments.test.js
new file mode 100644
index 00000000..5af11bfb
--- /dev/null
+++ b/backend/src/tests/comments.test.js
@@ -0,0 +1,220 @@
+"use strict";
+
+jest.mock("../db");
+jest.mock("../utils/logger", () => ({
+  info: jest.fn(),
+  warn: jest.fn(),
+  error: jest.fn(),
+  debug: jest.fn(),
+}));
+jest.mock("firebase-admin", () => ({ apps: [true], initializeApp: jest.fn() }));
+jest.mock("../middleware/appCheck", () => (req, res, next) => next());
+
+const request = require("supertest");
+const express = require("express");
+const jwt = require("jsonwebtoken");
+const db = require("../db");
+
+const JWT_SECRET = process.env.JWT_SECRET || "change-me-in-production";
+
+function makeToken(payload = {}) {
+  return jwt.sign({ sub: "WALLET123", ...payload }, JWT_SECRET);
+}
+
+function makeAdminToken() {
+  return jwt.sign({ sub: "ADMIN_WALLET", isAdmin: true }, JWT_SECRET);
+}
+
+const commentsRouter = require("../routes/comments");
+const commentActionsRouter = require("../routes/commentActions");
+
+const app = express();
+app.use(express.json());
+app.use("/api/markets/:id/comments", commentsRouter);
+app.use("/api/comments", commentActionsRouter);
+
+const makeComment = (id, overrides = {}) => ({
+  id,
+  market_id: 1,
+  wallet_address: "WALLET123",
+  content: "Test comment",
+  thumbs_up_count: 0,
+  created_at: new Date().toISOString(),
+  ...overrides,
+});
+
+describe("Market Comments API", () => {
+  beforeEach(() => jest.clearAllMocks());
+
+  // ── GET /api/markets/:id/comments ──────────────────────────────────────────
+  describe("GET /api/markets/:id/comments", () => {
+    it("returns paginated non-hidden comments", async () => {
+      const comments = [makeComment(1), makeComment(2)];
+      db.query
+        .mockResolvedValueOnce({ rows: comments })
+        .mockResolvedValueOnce({ rows: [{ total: "2" }] });
+
+      const res = await request(app).get("/api/markets/1/comments");
+
+      expect(res.status).toBe(200);
+      expect(res.body.comments).toHaveLength(2);
+      expect(res.body.meta).toMatchObject({ page: 0, pageSize: 20, total: 2 });
+    });
+
+    it("uses page query param for offset", async () => {
+      db.query
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [{ total: "0" }] });
+
+      await request(app).get("/api/markets/1/comments?page=2");
+
+      expect(db.query).toHaveBeenNthCalledWith(
+        1,
+        expect.stringContaining("OFFSET $3"),
+        [1, 20, 40]
+      );
+    });
+
+    it("returns 500 on db error", async () => {
+      db.query.mockRejectedValueOnce(new Error("DB down"));
+      const res = await request(app).get("/api/markets/1/comments");
+      expect(res.status).toBe(500);
+    });
+  });
+
+  // ── POST /api/markets/:id/comments ────────────────────────────────────────
+  describe("POST /api/markets/:id/comments", () => {
+    it("creates a comment with valid content", async () => {
+      const comment = makeComment(1);
+      db.query.mockResolvedValueOnce({ rows: [comment] });
+
+      const res = await request(app)
+        .post("/api/markets/1/comments")
+        .set("Authorization", `Bearer ${makeToken()}`)
+        .send({ content: "Hello world" });
+
+      expect(res.status).toBe(201);
+      expect(res.body.comment).toMatchObject({ id: 1 });
+    });
+
+    it("rejects missing content", async () => {
+      const res = await request(app)
+        .post("/api/markets/1/comments")
+        .set("Authorization", `Bearer ${makeToken()}`)
+        .send({});
+      expect(res.status).toBe(400);
+      expect(res.body.error).toMatch(/required/i);
+    });
+
+    it("rejects content over 500 chars", async () => {
+      const res = await request(app)
+        .post("/api/markets/1/comments")
+        .set("Authorization", `Bearer ${makeToken()}`)
+        .send({ content: "x".repeat(501) });
+      expect(res.status).toBe(400);
+      expect(res.body.error).toMatch(/500/);
+    });
+
+    it("rejects empty string content", async () => {
+      const res = await request(app)
+        .post("/api/markets/1/comments")
+        .set("Authorization", `Bearer ${makeToken()}`)
+        .send({ content: "   " });
+      expect(res.status).toBe(400);
+    });
+
+    it("requires JWT", async () => {
+      const res = await request(app).post("/api/markets/1/comments").send({ content: "Hello" });
+      expect(res.status).toBe(401);
+    });
+
+    it("rejects invalid JWT", async () => {
+      const res = await request(app)
+        .post("/api/markets/1/comments")
+        .set("Authorization", "Bearer invalid.token.here")
+        .send({ content: "Hello" });
+      expect(res.status).toBe(401);
+    });
+  });
+
+  // ── POST /api/comments/:id/thumbs-up ──────────────────────────────────────
+  describe("POST /api/comments/:id/thumbs-up", () => {
+    it("increments thumbs_up_count", async () => {
+      db.query
+        .mockResolvedValueOnce({ rows: [] }) // insert dedup
+        .mockResolvedValueOnce({ rows: [{ thumbs_up_count: 1 }] }); // update
+
+      const res = await request(app)
+        .post("/api/comments/1/thumbs-up")
+        .set("Authorization", `Bearer ${makeToken()}`);
+
+      expect(res.status).toBe(200);
+      expect(res.body.thumbs_up_count).toBe(1);
+    });
+
+    it("returns 409 on duplicate thumbs-up", async () => {
+      const dupErr = new Error("duplicate");
+      dupErr.code = "23505";
+      db.query.mockRejectedValueOnce(dupErr);
+
+      const res = await request(app)
+        .post("/api/comments/1/thumbs-up")
+        .set("Authorization", `Bearer ${makeToken()}`);
+
+      expect(res.status).toBe(409);
+      expect(res.body.error).toMatch(/already/i);
+    });
+
+    it("returns 404 when comment not found", async () => {
+      db.query.mockResolvedValueOnce({ rows: [] }).mockResolvedValueOnce({ rows: [] }); // no rows from UPDATE
+
+      const res = await request(app)
+        .post("/api/comments/999/thumbs-up")
+        .set("Authorization", `Bearer ${makeToken()}`);
+
+      expect(res.status).toBe(404);
+    });
+
+    it("requires JWT", async () => {
+      const res = await request(app).post("/api/comments/1/thumbs-up");
+      expect(res.status).toBe(401);
+    });
+  });
+
+  // ── DELETE /api/comments/:id ──────────────────────────────────────────────
+  describe("DELETE /api/comments/:id", () => {
+    it("sets is_hidden = TRUE (admin only)", async () => {
+      db.query.mockResolvedValueOnce({ rows: [{ id: 1 }] });
+
+      const res = await request(app)
+        .delete("/api/comments/1")
+        .set("Authorization", `Bearer ${makeAdminToken()}`);
+
+      expect(res.status).toBe(200);
+      expect(res.body.success).toBe(true);
+      expect(db.query).toHaveBeenCalledWith(expect.stringContaining("is_hidden = TRUE"), [1]);
+    });
+
+    it("returns 403 for non-admin JWT", async () => {
+      const res = await request(app)
+        .delete("/api/comments/1")
+        .set("Authorization", `Bearer ${makeToken()}`);
+      expect(res.status).toBe(403);
+    });
+
+    it("returns 404 when comment not found", async () => {
+      db.query.mockResolvedValueOnce({ rows: [] });
+
+      const res = await request(app)
+        .delete("/api/comments/999")
+        .set("Authorization", `Bearer ${makeAdminToken()}`);
+
+      expect(res.status).toBe(404);
+    });
+
+    it("requires JWT", async () => {
+      const res = await request(app).delete("/api/comments/1");
+      expect(res.status).toBe(401);
+    });
+  });
+});