Abstract: Schistosomiasis remains one of the most prevalent parasitic diseases in the sub-Saharan Africa including Ethiopia where Schistosoma mansoni and Schistosoma hematobium are widespread. praziquantel has been the most effective drug and used as mass chemotherapy. However, recently low cure rate recorded in different parts of the word. As it is the only drug used for schistosomiasis, there is a need to periodically evaluate the efficacy in different geographic settings. So this study evaluateed efficacy of Praziquantel against S.mansoni. Cross-sectional study was conducted in Fincha Valley followed by non randomized trial. Positive students treated with praziquantel 40mg/kg. Cure and reduction rate evaluated 4 weeks after treatment through fecal egg count by two Kato - Katz on two consecutive days. Data was analyzed and parasitological cure rate and egg reduction rate was 80.9% & 99.5% respectively. There was a significant association between cure rate and pre-treatment infection intensity (P > 0.05), but not between cure rate and age groups (P < 0.05). Praziquantel in a single dose remain efficacious despite prolonged use of the drug. However, further studies are needed.