Objective To study the presence of iNOS in Schistosoma japonicum and demonstrate its distribution in different stages of this schistosome. Methods Cryostat sections for adult worms and paraffin sections for eggs in the liver of infected mouse, sporocysts and cercariae in snails were prepared, immunofluorescent test was performed to detect the presence of iNOS in adult worms, sporocysts, cercariae and miracidium, the distribution of this enzyme was observed in different stages of Schistosoma japonicum. Western blotting was used to further demonstrate the immunoreactivity to iNOS in adult worms. Results The results of immunofluorescent test showed that specific yellow- green fluorescence was mainly among subtugment of adult worms. Positive staining was also distributed on the surface of miracidium and its glands. For both sporocysts and cercariae, the majority of fluorescence was on their surface. Anti-iNOS antibody could recognize an apparent specific band in Western blotting of adult worm proteins, with a of Mr 210 000. Conclusion There is an expression of iNOS-like enzyme in Schistosoma japonicum.