OBJECTIVE To evaluate the effects of arsenic trioxide (As2O3) on the cell cycle and microfilament cytoskeleton in human nasopharyngeal carcinoma cell line(CNE1),as well as possible mechanisms. METHODS The variation of cell cycle and microfilament cytoskeleton in CNE1 were observed using the flow cytometry (FCM),the laser scanning confocal microscopy(LSCM)and technology of fluorescence.RESULTS FCM showed that the proportion of G1 phase cells significantly increased in cells exposed to 2 and 4?mol/L As2O3(P