Objective To study the molecular mechanism of apoptosis of cells in egg granuloma induced by anti-idiotypic antibody NP30 of Schistosoma japonicum.Methods BALB/c mice were randomly divided into two groups. The mice of the experimental group were immunized by injecting NP30 intraperitoneally for three times, while the mice of control group were injected normal saline intraperitoneally. The mice were sacrificed respectively on the 39th, 49th, 64th, 108th, 112nd day after challenge with schistosome cercariae. The expressions of apoptosis-related gene Bax, Bcl-2, death receptor Fas, FasL (Fas ligand) and c-Fos were examined by the S-P method of immunohistochemistry,and Bax, mRNA and Fas mRNA investigated by the in-situ hybridization. Results The expressions of Bax, Fas, FasL and c-Fos were positive in granuloma cells of both groups. The expressions of Bax and FasL in experimental group were higher than those in control group (P