A sensitive and specific immunoblot assay was used to analyze 33 cases of immune reactions between sera of Schistosomiasis Japonica patients and schistosome Japonicum egg (SEA) and adult (SWAP) antigens. The assays consists of SDS-PAGE and Western blot. The sensitivity of SEA reaction is 100%, while that of SWAP is 97%, with negative reactivity in the control sera. In most cases (28/33), SEA reactive to patient sera show three wide bands at 180,54 and 32kD while in the case of SWAP it shows two wide bands at 190 and 64kD in 26 cases(26/32). In most patients (21/24) with acute schistosomiasis Japonica, an additional wide band is seen at 34kD. These results suggest clinical value of Western Blot in the diagnosis of schistosomiasis Japonica.