Abstract: OBJECTIVE To evaluate the effect of chitosan nanoparticles on the proliferation of K562 cells, and to explore the related mechanism. METHODS The best time and concentration of chitosan nanoparticles were screened by MTT method. Immunofluorescence and transmission electron microscope were used to study the effect of chitosan nanoparticles on the morphology of K562 cells. FACS was used to detect the effect of chitosan nanoparticles on MMP, intracellular ROS concentration, and Ca²⁺ concentration. RESULTS Chitosan nanoparticles(15 μg·mL^-1) could induce K562 cells apoptosis, such as nuclei smaller, nuclear condensation phenomena, company with the collapse of mitochondrial membrane potential, increased ROS content, and the increased of Ca²⁺ concentration. CONCLUSION Chitosan nanoparticles can inhibit the proliferation of K562 cells, the mechanism may be related to inducing cell apoptosis.