AIM: To observe the effect of antiembryonation and anti-female fecundity immunity in mice induced by the 26/28 kDa antigens purified from soluble immature eggs antigen (SIEA) of Schistosoma japonicum. METHODS: BALB/c mice were immunized with SIEA 26/28 kDa or SIEA-I antigen to examine if these antigens can induce anti-disease immunity as determined by egg burden in liver, intestines and faeces on day 46 after challenge infection with cercariae of S. japo icum. RESULTS: A comparison of the egg burden in tissues and faeces on day 46 after challenge infection showed that the number of mature eggs in the livers, intestines and faeces was significantly reduced in mice immunized with SIEA 26/28kDa by 83.6%, 93.3% and 87.3%, respective-ly, whereas the number of dead eggs was much greater in the tissues of immunized mice than in that of control mice. In addition, the number of eggs in the uteri of female adults was obviously decreased in mice immunized with SIEA 26/28 kDa antigens or with the SIEA. However, these immune responses were not induced by the SEA or SIEA-I. CONCLUSION: The 26/28 kDa antigens were major components in SIEA responsible for both anti-fecundity and antiembryonation immunity.