Tamoxifen (Tam) has a broad spectrum of anticancer activity, but is limited in clinical application. The aim of this study was to explore the smart pH-responsive drug delivery system (DDS) based on chitosan (CH) nanoparticles (NPs) for its potential in enabling more intelligent controlled release and enhancing chemotherapeutic efficiency of Tamoxifen. Tamoxifen was loaded onto CH-nanoparticles by forming complexes and Tamoxifen was released from the DDS much more rapidly at pH 4.0 and 6.0 than at pH 7.4, which is a desirable characteristic for tumor-targeted drug delivery. Tamoxifen-loaded CH nanoparticles induced remarkable improvement in anticancer activity, as demonstrated by MTT-assay, AO/EtBr and Hoechst nuclear staining. Furthermore, the possible signaling pathway was explored by RT-PCR. For instance, in human breast cancer MCF-7 cells, it was demonstrated that Tamoxifen-loaded CH nanoparticles increase intracellular concentration of Tamoxifen and enhance its anticancer efficiency by inducing apoptosis in a caspase-dependent manner, indicating that drug loaded nanoparticles could act as an efficient DDS importing Tamoxifen into target cancer cells.