Objective To investigate the effect of Toxoplasma gondii ME49 strain on the apoptosis of mouse placental trophoblastic cells in vitro.Methods Mouse placental trophoblastic cells (concentration of 5×106/ml) were cultured in the different cell culture vessels. The cells were treated for 8 h with different concentrations of Toxoplasma gondii ME49 strain (the concentration of tachyzoites was 2×106 /ml, 4×106 /ml, and 8×106/ml, respectively). FCM was used to examine the apoptosis rates of the placental trophoblastic cells stained with the fluorescent dye of Annexin Ⅴ-FITC/PI; fluorescence microscopy was used to observe the changes of cellular morphology, and Western blotting analysis was used to detect the protein levels of Bax and Bcl-2. Results The trophoblastic cells infected with Toxoplasma gondii ME49 strain showed a higher apoptosis compared to the normal cells(P<0.05), and the apoptosis rates increased with the concentration of tachyzoites in the infected groups. The highest apoptosis rate was 28.37% which was found 8 h after culture with 8×106 /ml tachyzoites. Fluorescence microscope observed that the apoptosis of trophoblastic cells increased with the increase of Toxoplasma gondii. Western blotting analysis showed that the relative expression levels of Bax and Bcl-2 were 1.24±0.05, 1.37±0.03, 1.78±0.04, and 1.15±0.03, 1.09±0.05, 0.97±0.01, respectively, which were significantly different from those of the control group (1.17±0.06, 1.23±0.02, P<0.05). Conclusion Infection with Toxoplasma gondii ME49 strain can promote the apoptosis of mouse placental trophoblastic cells in vitro through up-regulating Bax expression and down-regulating Bcl-2 expression.