Thirty Kunming mice were randomly divided into three groups named as dihydroartemisining roup(A),dihydroartemisinin and azithromycin group(B), and controlgroup(C). Each mouse was infected intraperitoneally with 2×10³ Toxoplasma gondii tachyzoites. Eight hours after infection, the mice of groups A and B were treated twice a day for 4 days with 75 mg/kg of dihydroartemisinin. At 24 hours post infection, those in group B were treated once daily for 4 days with 200 mg/kg of azithromycin. At 96 hours post infection, ascites was taken from one mouse each group and the tachyzoites were collected. The ultrastructure of tachyzoites was observed by conventional transmission electron microscopy. It was found that the tachyzoites in groups A and B showed edema and enlarged，the cell membrane became indistinct， broken or damaged; fat droplets in the cytoplasm increased, and vacuoles were formed. Similar changes were not seen in the control group.