A new approach has been developed for the synthesis of Au@CdS core-shell nanoparticles (CSNs) by a directly self-assembling process. Stable Au@CdS composite colloids were prepared by thiourea, as a double functional reagents acted as the linkage agent between Cd2+ ions and gold nanoparticles. The CdS-capped gold composite nanoparticles were successfully integrated into BaTiO3 films. The third-order nonlinear optical properties of Au@CdS CSNs have been studied using femtosecond optical Kerr effect (OKE) technology at 800 nm. The significant enhancement of nonresonant third-order nonlinear optical nonlinearities of Au@CdS CSNs was reported for the first time. (C) 2003 Elsevier Science B.V. All rights reserved.