The inhibitory effects of Tanshinon IIA on human osteosarcoma MG-63 cell proliferation have been studied using the methods of cell culture,life cells refuse trypan blue dye count,optic microscope observe,flow cytometry analysis,and immuncytochemistry technology.The results showed that proliferation of human osteosarcoma cell could be inhibited by Tanshinone II A,and the inhibitory rate is 52.10%.The cell-twofold-time is prolonged from 48 h to 65 h.The results of flow cytometry analysis showed that MG-63 cells were arrested in G0/G1 phase;the proportion of the cells in G0/G1 phase rose from 47.5% to 59.5% and that of the cells in S phase declined from 20.0% to 9.0%.The morphology of the cell was regular and their size appeared similar,down regulation of gene products required for proliferation(c-fos,c-myc).Our study suggested that Tanshinon IIA had stronger inhibitory effect on human osteosarcoma MG-63 cell,the molecular mechanism might be relationship with Tanshinon IIA down regulation the oncogene c-fos and c-myc and therefore regulation cell cycle