Abstract: The amphipathic poly（N-phenylmaleimide）-b-poly（4-vinylpyridine）-Cd²⁺（PNPV-Cd²⁺） complex has been synthesized by reversible addition fragmentation chain transfer（RAFT） polymerization.The 4VP groups acted as the coordination sites for cadmium ion aggregations and nanosized CdS particles were successfully grown in situ at these sites with the release of S2-ions from thioacetamide.The CdS content and size in poly（N-phenylmaleimide）-b-poly（4-vinylpyridine）-CdS（PNPV-CdS） nanocomposites were controlled by the polymerization time.The optical properties of the prepared PNPV-CdS nanocomposites were characterized by linear absorption and photoluminescence（PL） spectra.The PL properties of the nanocomposites are controllable by RAFT method.Z-scan measurement was also employed to investigate the third-order nonlinear optical（NLO） properties at a wavelength of 532 nm.The nonlinear optical response of PNPV-CdS is much stronger than that of CdS and PNPV.This nanocomposite has potential applications in all-optical switches in optical information processing.