Abstract: 【Abstract】 MCF-7，DU-145，EC109 and A549 tumor cells （5×104/ml） at mid-exponential phase were treated for 24 h with different concentrations of Toxoplasma gondii tachyzoites（1×10⁴/ml-32×10⁴/ml）. The measurement of tumor cell growth inhibition rate was performed by using CCK-8 kit. The tachyzoites （1×10⁴/ml-4×10⁴/ml） were co-cultured with A549 tumor cells for 24 h. Flow cytometry techniques was applied to investigate the expression of p53 and Bcl-2. The results showed a remarkable inhibitory effect of the parasites on tumor cell proliferation，which presented a dosage dependence. MCF-7，DU-145，EC-109 and A549 cell lines treated with 1×10⁴/ml T. gondii tachyzoites presented an inhibition rate of 19.7%，4.5%，28.0%，and 20.8%，respectively. There was a significant difference between experimental groups and the control （P<0.05）. T. gondii induced cell apoptosis in A549 tumor cells. p53 and Bcl-2 gene expression was respectively up-regulated and down-regulated.

Key words: Toxoplasma gondii, Tumor cell, Flow cytometry, CCK-8 method