Schistosomiases, the major public health problem in rural Egypt, with almost six million people were infected so the early diagnosis is essential for adequate treatment of acute infection. In this study, we compare PCR and Western blot techniques in diagnosis of schistosomiasis mansoni. Forty Swiss albino mice were used, thirty two mice were infected with cercariae of S. mansoni and eight mice were kept non infected which were used as a control. Blood was obtained from four infected mice weekly beginning from the 1st week to the 8th week post infection. PCR and Western blot techniques were performed on this blood. We found that PCR was positive from the first week post infection and the strips appeared at 110 pb, while Western blot technique was positive from the second week post infection and the antibodies reaction against protein bands appeared at 130, 95, 55, 43 and 32KDa. From these results, we found that PCR can diagnose schistosomiasis mansoni earlier than Western blot technique.