diff --git a/mem0-ts/src/client/mem0.types.ts b/mem0-ts/src/client/mem0.types.ts
index 185b1dbea..ba778415d 100644
--- a/mem0-ts/src/client/mem0.types.ts
+++ b/mem0-ts/src/client/mem0.types.ts
@@ -169,7 +169,9 @@ export interface PaginatedMemories {
 
 export interface ProjectResponse {
   customInstructions?: string;
-  customCategories?: string[];
+  // The API returns category objects (`[{ "<name>": "<description>" }]`),
+  // not bare strings (see issue #5738).
+  customCategories?: custom_categories[];
   [key: string]: any;
 }
 
diff --git a/mem0-ts/src/client/tests/utils.test.ts b/mem0-ts/src/client/tests/utils.test.ts
index 9007a6b87..d76385845 100644
--- a/mem0-ts/src/client/tests/utils.test.ts
+++ b/mem0-ts/src/client/tests/utils.test.ts
@@ -99,4 +99,50 @@ describe("camelToSnakeKeys / snakeToCamelKeys", () => {
       });
     });
   });
+
+  describe("user-controlled customCategories names (issue #5738)", () => {
+    it("converts the outer key but leaves multi-word category names on write", () => {
+      expect(
+        camelToSnakeKeys({
+          customCategories: [
+            { work_life_balance: "desc" },
+            { AIResearch: "desc" },
+          ],
+        }),
+      ).toEqual({
+        // outer SDK key is snake_cased, user-defined category names are not
+        custom_categories: [
+          { work_life_balance: "desc" },
+          { AIResearch: "desc" },
+        ],
+      });
+    });
+
+    it("converts the outer key but leaves category names verbatim on read", () => {
+      expect(
+        snakeToCamelKeys({
+          custom_categories: [
+            { work_life_balance: "desc" },
+            { AIResearch: "desc" },
+          ],
+        }),
+      ).toEqual({
+        customCategories: [
+          { work_life_balance: "desc" },
+          { AIResearch: "desc" },
+        ],
+      });
+    });
+
+    it("round-trips category names losslessly (write then read)", () => {
+      const customCategories = [
+        { work_life_balance: "balance between work and life" },
+        { AIResearch: "artificial intelligence research" },
+      ];
+      const roundTripped = snakeToCamelKeys(
+        camelToSnakeKeys({ customCategories }),
+      );
+      expect(roundTripped.customCategories).toEqual(customCategories);
+    });
+  });
 });
diff --git a/mem0-ts/src/client/utils.ts b/mem0-ts/src/client/utils.ts
index 817dd02cf..aca9ffbcd 100644
--- a/mem0-ts/src/client/utils.ts
+++ b/mem0-ts/src/client/utils.ts
@@ -29,6 +29,11 @@ const OPAQUE_VALUE_KEYS = new Set([
   "metadata",
   "structuredDataSchema",
   "structured_data_schema",
+  // Custom-category names are user-controlled keys (`[{ "<name>": "<desc>" }]`).
+  // Listed in both casings so they round-trip verbatim in both directions
+  // (see issue #5738; same class as `metadata`/`structuredDataSchema`).
+  "customCategories",
+  "custom_categories",
 ]);
 
 /**