diff --git a/sdk/src/index.ts b/sdk/src/index.ts
index b1ea0de..7adfcc3 100644
--- a/sdk/src/index.ts
+++ b/sdk/src/index.ts
@@ -383,6 +383,31 @@ export class StellarRWASDK {
     this.logger.info('SDK initialized successfully');
   }
 
+  /**
+   * Serialize any value (SDK result, portfolio, order book, …) to a
+   * JSON-safe structure with every BigInt rendered as a decimal string.
+   * Use this when returning SDK data from a JSON HTTP API. (Issue #193)
+   */
+  toJSONSafe<T = any>(value: T): any {
+    return serializeBigInts(value);
+  }
+
+  /**
+   * `JSON.stringify` with lossless BigInt support (tagged `{"$bigint":"n"}`
+   * format restored by {@link StellarRWASDK.parseJSON}). (Issue #193)
+   */
+  stringifyJSON(value: any, space?: string | number): string {
+    return stringifyJSON(value, space);
+  }
+
+  /**
+   * `JSON.parse` that restores BigInt values produced by
+   * {@link StellarRWASDK.stringifyJSON}. (Issue #193)
+   */
+  parseJSON<T = any>(text: string): T {
+    return parseJSON<T>(text);
+  }
+
   /**
    * Create a token client for a specific RWA token
    */
diff --git a/sdk/src/types.ts b/sdk/src/types.ts
index 42ceb0d..adea21a 100644
--- a/sdk/src/types.ts
+++ b/sdk/src/types.ts
@@ -682,3 +682,129 @@ export interface WebhookConfig {
   events: string[];
   active: boolean;
 }
+
+// ---------------------------------------------------------------------------
+// BigInt JSON serialization (Issue #193)
+// ---------------------------------------------------------------------------
+//
+// `JSON.stringify` throws on `bigint` values. These helpers make BigInt safe to
+// send over a JSON API and to parse back losslessly.
+//
+// Two modes:
+//   1. Plain-string mode (`bigIntReplacer`) — every BigInt becomes a decimal
+//      string. Use for external API responses where the consumer treats large
+//      integers as strings. Round-tripping requires knowing which fields are
+//      BigInt (see `createBigIntReviver`).
+//   2. Tagged mode (`stringifyJSON` / `parseJSON`) — every BigInt becomes
+//      `{"$bigint":"<decimal>"}`, which `parseJSON` restores to a real BigInt.
+//      Use for internal persistence / caches that must round-trip exactly.
+
+/** Marker key used by the tagged serialization format. */
+export const BIGINT_TAG = '$bigint' as const;
+
+export interface TaggedBigInt {
+  [BIGINT_TAG]: string;
+}
+
+export function isTaggedBigInt(value: unknown): value is TaggedBigInt {
+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    typeof (value as any)[BIGINT_TAG] === 'string' &&
+    Object.keys(value as any).length === 1
+  );
+}
+
+/**
+ * `JSON.stringify` replacer that renders every `bigint` as a decimal string.
+ * Also normalises `BigInt`-like objects (e.g. `bignumber.js`) via `toString()`
+ * when they expose an `isBigNumber`/`_isBigNumber` flag.
+ */
+export function bigIntReplacer(_key: string, value: any): any {
+  if (typeof value === 'bigint') return value.toString();
+  if (
+    value &&
+    typeof value === 'object' &&
+    (value._isBigNumber === true || value.isBigNumber === true) &&
+    typeof value.toString === 'function'
+  ) {
+    return value.toString();
+  }
+  return value;
+}
+
+/**
+ * `JSON.stringify` replacer for the tagged format: `bigint` -> `{$bigint: "n"}`.
+ */
+export function taggedBigIntReplacer(_key: string, value: any): any {
+  return typeof value === 'bigint' ? { [BIGINT_TAG]: value.toString() } : value;
+}
+
+/**
+ * `JSON.parse` reviver for the tagged format: `{$bigint: "n"}` -> `bigint`.
+ */
+export function bigIntReviver(_key: string, value: any): any {
+  return isTaggedBigInt(value) ? BigInt(value[BIGINT_TAG]) : value;
+}
+
+const BIGINT_STRING_RE = /^-?\d+$/;
+
+/**
+ * Build a `JSON.parse` reviver that converts the string value of the named keys
+ * back into `bigint`. Use with output produced by {@link bigIntReplacer} when
+ * the BigInt-bearing field names are known.
+ *
+ * @param keys Field names whose string values should become BigInt.
+ * @param options.onlyUnsafe Only convert when the number exceeds
+ *        `Number.MAX_SAFE_INTEGER` (default: false — always convert).
+ */
+export function createBigIntReviver(
+  keys: Iterable<string>,
+  options: { onlyUnsafe?: boolean } = {}
+): (key: string, value: any) => any {
+  const keySet = new Set(keys);
+  return (key: string, value: any) => {
+    if (isTaggedBigInt(value)) return BigInt(value[BIGINT_TAG]);
+    if (typeof value === 'string' && keySet.has(key) && BIGINT_STRING_RE.test(value)) {
+      if (options.onlyUnsafe && Number.isSafeInteger(Number(value))) return value;
+      return BigInt(value);
+    }
+    return value;
+  };
+}
+
+/**
+ * Recursively convert every `bigint` in a value to a decimal string. Handles
+ * nested objects, arrays, `Map` and `Set`. Non-mutating.
+ */
+export function serializeBigInts<T = any>(input: T): any {
+  if (typeof input === 'bigint') return input.toString();
+  if (Array.isArray(input)) return input.map((v) => serializeBigInts(v));
+  if (input instanceof Map) {
+    const out: Record<string, any> = {};
+    for (const [k, v] of input) out[String(k)] = serializeBigInts(v);
+    return out;
+  }
+  if (input instanceof Set) return [...input].map((v) => serializeBigInts(v));
+  if (input && typeof input === 'object') {
+    if (input instanceof Date) return input;
+    const out: Record<string, any> = {};
+    for (const [k, v] of Object.entries(input)) out[k] = serializeBigInts(v);
+    return out;
+  }
+  return input;
+}
+
+/**
+ * `JSON.stringify` with lossless BigInt support (tagged format).
+ */
+export function stringifyJSON(value: any, space?: string | number): string {
+  return JSON.stringify(value, taggedBigIntReplacer, space);
+}
+
+/**
+ * `JSON.parse` that restores BigInt values written by {@link stringifyJSON}.
+ */
+export function parseJSON<T = any>(text: string): T {
+  return JSON.parse(text, bigIntReviver) as T;
+}