diff --git a/src/core/Multicall.ts b/src/core/Multicall.ts
index 90e794c5..13329a0d 100644
--- a/src/core/Multicall.ts
+++ b/src/core/Multicall.ts
@@ -1,4 +1,4 @@
-import { WhiteChainError } from "../types.js";
+import { ValidationError, WhiteChainError } from "../errors/index.js";
 import type {
   Multicall3Call,
   Multicall3CallResult,
@@ -19,6 +19,34 @@ export const AGGREGATE3_SELECTOR = "0x82ad56cb";
 
 export type RpcFetchFn = (method: string, params: any[]) => Promise<any>;
 
+/**
+ * Returns true when a raw calldata string is 0x-prefixed, byte-aligned hex.
+ */
+export function isValidHexData(data: string): data is `0x${string}` {
+  return typeof data === "string" && /^0x(?:[0-9a-fA-F]{2})*$/.test(data);
+}
+
+function assertValidHexData(data: string, label: string): `0x${string}` {
+  if (typeof data !== "string") {
+    throw new ValidationError(`${label} must be a hex string.`);
+  }
+
+  if (!data.startsWith("0x")) {
+    throw new ValidationError(`${label} must start with 0x.`);
+  }
+
+  const rawData = data.slice(2);
+  if (rawData.length % 2 !== 0) {
+    throw new ValidationError(`${label} must contain an even number of hex characters.`);
+  }
+
+  if (!/^[0-9a-fA-F]*$/.test(rawData)) {
+    throw new ValidationError(`${label} contains non-hex characters.`);
+  }
+
+  return data as `0x${string}`;
+}
+
 /**
  * Encodes an array of Multicall3Call objects into ABI-compliant aggregate3 calldata.
  */
@@ -50,7 +78,7 @@ export function encodeAggregate3(
     const targetAddrPadded = call.target.toLowerCase().replace(/^0x/, "").padStart(64, "0");
     const allowFailurePadded = (allowFailure ? 1 : 0).toString(16).padStart(64, "0");
 
-    const rawCallData = call.callData.replace(/^0x/, "");
+    const rawCallData = assertValidHexData(call.callData, `calls[${i}].callData`).slice(2);
     const callDataLenHex = (rawCallData.length / 2).toString(16).padStart(64, "0");
 
     // Pad callData to 32-byte boundary
diff --git a/tests/core/Multicall.test.ts b/tests/core/Multicall.test.ts
index 583c8046..1c1934c1 100644
--- a/tests/core/Multicall.test.ts
+++ b/tests/core/Multicall.test.ts
@@ -5,7 +5,9 @@ import {
   DEFAULT_MULTICALL3_ADDRESS,
   encodeAggregate3,
   decodeAggregate3Results,
+  isValidHexData,
 } from "../../src/core/Multicall.js";
+import { ValidationError } from "../../src/errors/index.js";
 import { WhiteChainError } from "../../src/types.js";
 import type { Multicall3Call } from "../../src/types/multicall.js";
 
@@ -131,6 +133,27 @@ describe("Multicall", () => {
     expect(results[1].value).toBeUndefined();
   });
 
+  it("validates raw calldata before encoding aggregate3 payloads", () => {
+    const target = "0x1111111111111111111111111111111111111111";
+
+    expect(isValidHexData("0x")).toBe(true);
+    expect(isValidHexData("0x70a08231")).toBe(true);
+    expect(isValidHexData("0x70A08231")).toBe(true);
+    expect(isValidHexData("70a08231")).toBe(false);
+    expect(isValidHexData("0xabc")).toBe(false);
+    expect(isValidHexData("0xzz")).toBe(false);
+
+    expect(() => encodeAggregate3([{ target, callData: "70a08231" as any }])).toThrow(
+      ValidationError
+    );
+    expect(() => encodeAggregate3([{ target, callData: "0xabc" as any }])).toThrow(
+      "calls[0].callData must contain an even number of hex characters."
+    );
+    expect(() => encodeAggregate3([{ target, callData: "0xzz" as any }])).toThrow(
+      "calls[0].callData contains non-hex characters."
+    );
+  });
+
   it("throws WhiteChainError if input calls array is empty or eth_call fails", async () => {
     const mockFetchFn = vi.fn().mockResolvedValue(null);
     const multicall = new Multicall(mockFetchFn);