Abstract: 90 mice were randomly divided into six groups: nomal control，infected control，long-term drug use group 1(L1)，long-term drug use group 2(L2)，short-term drug use group 1(S1)and short-term drug use group 2(S2). Mice in all groups except those in the nomal control group were infected with 30 cercariae of Schistosoma japonicum through abdominal skin. N-acetylcysteine（NAC）solution was orally given to mice in L1 and L2 groups，200 mg/kg and 400 mg/kg，respectively，2 times/d from the day of infection，while for S1 and S2 groups，200 mg/kg and 400 mg/kg，respectively，2 times/d from the 42th day after L2 infection. Mice in the groups of nomal control，infected control，L1 and L2 were sacrificed either on day 42 or day 56 after infection，while those in S1 and S2 were sacrificed on day 56 after infection. Number and area of the single egg granuloma were measured with computer image analysis software. The concentration of malondialdehyde（MDA）and the activity of superoxide dismutase（SOD）in serum and hepatic tissue were detected. The number of“+”single egg granulomas in the liver of mice in L1 was the fewest by 3.04，followed by those in S1，by 4.87. The results indicated that the level of MAD in hepatic tissue of L2（9.2-9.3 nmol/mg）was markedly lower than that of L1（P＜0.05），and the level of SOD in hepatic tissue of L1 was 170.00-190.00 U/(g·pro)，similar to those of S1 and L2 at the 42th day（P＞0.05），but the level in L2 at the 56th day was close to that of S2（P＞0.05）. Hence，NAC may retard the formation of single egg granulomas in the liver of infected mice，and may regulate the concentration of MDA and the activity of SOD in the liver.

Key words: N-acetylcysteine；Schistosoma , japonicum；Superoxide dismutase；Malondialdehyde