MCF-7, DU-145, EC-109 and A549 tumor cells (5 x 10(4)nml) at mid-exponential phase were treated for 24h with different concentrations of Toxoplasma gondii tachyzoites (1 x 10(4)/ml-32x10(4)/ml). The measurement of tumor cell growth inhibition rate was performed by using CCK-8 kit. The tachyzoites (1 x 10(4)/ml-4 x 10(4)/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 x 10(4) 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.