Objective To explore the activity of heme oxygenase and immunolocate the enzyme in the adult worms of Schistosoma japonicum .Methods Microsomal protein was isolated from the homogenate of adult S\^japonicum , heme degradation and effect of different pH conditions and buffers on degrading reaction were investigated by incubating microsomal protein with hemin. The slices of whole worm and cells of S\^japonicum were prepared, distribution of HO in schistosome was studied by immunofluorescent and alkaline phosphatase(AP) \|immunocytochemical assays.Results Microsomal protein of adult worms can degrade the heme in vitro , the activity being 56\^7 nmol bilirubin/(mg?min).The optimal pH was 8\^7. Immunofluorescent and AP\|immunocytochemical assays revealed that the HO distributed dispersively in the worm, and located in cytoplasm.Conclusion The presence of HO was firstly proved in S\^japonicum .