Objective: To prepare sinomenine hydrochloride-loaded chitosan nanoparticles and investigate their characteristics and in vitro drug release ability. Method: The nanoparticles were prepared by microemulsion-ionic crosslinking method with Na5P3O10 used as crosslinkers.The morphology of nanoparticles was evaluated by the transmission electron microscopy (TEM).The mean size and zeta potential of nanoparticles were determined by dynamic light scattering (DLS).The in vitro release of the drug-loaded chitosan nanoparticles was evaluated using a dialysis method. Result: The nanoparticles were successfully prepared with the spherical or para-spherical shape.Their mean diameter was 98.3 nm.The encapsulation efficiency was 67.2%.The release experiment of drug in vitro showed that the release rate of drug-loaded nanoparticles was stable and sustained for 24 hours. Conclusion: The preparation method is reliable and simple.The nanoparticles possessed good physical performance and sustained release character in vitro .