Abstract: A circulating schistosome 70kDa antigen (SJ 70) has been detected in sera of mice infected with Schistosoma japonteum. using a double antibody sandwich enzyme-linked immunoabsorbent assay (ELISA). SJ 70 antigen was first detected in the sera of S. ja-poreicum-infected mice at the 4th week after infection and increased rapidly, reaching their peak by the 7th week after infection, and remaining relatively unchanged for additional 9 weeks. In contrast, in mice infected with S. japonicum for 7 weeks and then treated with praziquantel (100mg/kg body weight) there was a significant decrease in serum antigen levels within two weeks after treatment. An almost complete disappearance of the antigen from the sera occurred by the 5th week after treatment.The results indicated that the detection of SJ 70 antigen might be used as early diagnosis of schistosoniasis and evaluation of drug efficacy