Abstract: OBJECTIVE To prepared arsenic trioxide solid liguid nanoparticles with central composite design and study the inhibitory effect of arsenic trioxide solid liqid nanoparticles on four kinds of tumor cells. METHODS Arsenic trioxide solid lipid nanoparticles were prepared by emulsion-ultrasonic dispersion method. And MTT experiment was used to investigate the inhibition of four tumor cells. RESULTS The optimal formulation was screened as monostearin 0.11 g and soy lecithin 0.18 g. Average size of nanoparticles was 131.54 nm. Encapsulation efficiency was 73.46% and drug loading was 1.07%. The proliferations of four cells were inhibited by different concentrations of arsenic trioxide. And nanoparticles further induced the apoptosis of cells. CONCLUSION Arsenic trioxide solid lipid nanoparticles prepared by emulsion-ultrasonic dispersion method owned well stability and uniformity of particle distribution which meets pharmaceutical requirement. The inhibitory effect of arsenic trioxide solid lipid nanoparticles carrying cationic potential is the most notable.