The study was purposed to investigate the growth inhibitory effect of tanshinones on K562 cell line and the relationship between their structures and cytotoxicity. The modified MTT assay was adopted to measure the inhibitory effect of tanshinones at different concentrations and chemical structures on K562 cells, and the changes of cell morphology were observed by inverted phase contrast microscopy. The results indicated that the tanshinones could inhibit the proliferation of K562 cells effectively, and their cytotoxicities on K562 cells showed concentration- and time-dependent manners. The IC(50) of dihydrotanshinone I, tanshinone I, tanshinone IIA and cryptotanshinone at 24 hours were 0.91, 4.04, 5.95, 13.85 µg/ml at 48 hours were 0.37, 1.35, 1.71, 6.71 µg/ml; at 72 hours were 0.33, 0.46, 0.82, 6.02 µg/ml, respectively. It is concluded that all of the four tanshinones have proliferation inhibitory effect on K562 cell line, among them the dihydrotanshinone I is the most active one, followed by tanshinone I, tanshinone IIA and cryptotanshinone subsequently, indicating that the chemical structure of aromatic ring A of tanshinones can enhance their cytotoxicity and the structure of furan ring C may influence the cytotoxicity, but their mechanism is still remained to be further investigated.