diff --git a/apps/web/src/features/wallet/components/NetworkMismatchBanner.test.tsx b/apps/web/src/features/wallet/components/NetworkMismatchBanner.test.tsx
new file mode 100644
index 0000000..c0bcdb0
--- /dev/null
+++ b/apps/web/src/features/wallet/components/NetworkMismatchBanner.test.tsx
@@ -0,0 +1,125 @@
+import { describe, it, expect, beforeEach, afterEach, beforeAll, vi } from "vitest"
+import { render, screen, fireEvent } from "@testing-library/react"
+import { useWalletStore } from "../store/wallet-store"
+import { NetworkMismatchBanner } from "./NetworkMismatchBanner"
+import { NETWORK } from "@/app/config/network"
+
+// ── Mock router ──────────────────────────────────────────────────────────────
+const mockLocation = { pathname: "/faucet" }
+
+vi.mock("@tanstack/react-router", () => ({
+  useLocation: () => mockLocation,
+}))
+
+describe("NetworkMismatchBanner (#211)", () => {
+  let originalNetworkName: "testnet" | "mainnet"
+
+  beforeAll(() => {
+    originalNetworkName = NETWORK.name
+  })
+
+  beforeEach(() => {
+    // Clear sessionStorage and reset mock defaults
+    sessionStorage.clear()
+    mockLocation.pathname = "/faucet"
+    NETWORK.name = "testnet"
+
+    // Default wallet state: connected to testnet
+    useWalletStore.setState({
+      address: "GAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWHF",
+      walletId: "freighter",
+      status: "connected",
+      pendingTransactionXdr: null,
+      network: "testnet",
+    })
+  })
+
+  afterEach(() => {
+    vi.restoreAllMocks()
+    NETWORK.name = originalNetworkName
+  })
+
+  it("does not render when networks match (both testnet)", () => {
+    render(<NetworkMismatchBanner />)
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument()
+  })
+
+  it("does not render when wallet is disconnected", () => {
+    useWalletStore.setState({
+      address: null,
+      walletId: null,
+      status: "disconnected",
+      network: "testnet",
+    })
+    render(<NetworkMismatchBanner />)
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument()
+  })
+
+  it("does not render on landing page (pathname = '/') even with mismatch", () => {
+    mockLocation.pathname = "/"
+    NETWORK.name = "mainnet" // Mismatch: app mainnet vs wallet testnet
+    render(<NetworkMismatchBanner />)
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument()
+  })
+
+  it("renders warning banner when app is testnet and wallet is mainnet", () => {
+    // Wallet mainnet, App testnet
+    useWalletStore.setState({
+      address: "GAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAWHF",
+      walletId: "freighter",
+      status: "connected",
+      network: "mainnet",
+    })
+
+    render(<NetworkMismatchBanner />)
+
+    const alert = screen.getByRole("alert")
+    expect(alert).toBeInTheDocument()
+    expect(
+      screen.getByText(
+        /Your wallet is connected to Mainnet but this app is running on Testnet\. Please switch networks in your wallet\./i,
+      ),
+    ).toBeInTheDocument()
+  })
+
+  it("renders warning banner when app is mainnet and wallet is testnet", () => {
+    // Wallet testnet, App mainnet
+    NETWORK.name = "mainnet"
+
+    render(<NetworkMismatchBanner />)
+
+    const alert = screen.getByRole("alert")
+    expect(alert).toBeInTheDocument()
+    expect(
+      screen.getByText(
+        /Your wallet is connected to Testnet but this app is running on Mainnet\. Please switch networks in your wallet\./i,
+      ),
+    ).toBeInTheDocument()
+  })
+
+  it("dismisses the banner when the Dismiss button is clicked", () => {
+    NETWORK.name = "mainnet" // Wallet testnet vs App mainnet
+
+    const { rerender } = render(<NetworkMismatchBanner />)
+
+    expect(screen.getByRole("alert")).toBeInTheDocument()
+
+    const dismissButton = screen.getByRole("button", { name: /Dismiss/i })
+    fireEvent.click(dismissButton)
+
+    // Alert should immediately disappear from DOM
+    rerender(<NetworkMismatchBanner />)
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument()
+
+    // Assert that sessionStorage was updated
+    expect(sessionStorage.getItem("so4-network-mismatch-dismissed")).toBe("1")
+  })
+
+  it("respects pre-existing dismissal state from sessionStorage", () => {
+    NETWORK.name = "mainnet" // Wallet testnet vs App mainnet
+    sessionStorage.setItem("so4-network-mismatch-dismissed", "1")
+
+    render(<NetworkMismatchBanner />)
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument()
+  })
+})