Schistosomiasis is one of the major health problems in many developing countries and causes liver damage. In addition, under the influence of schistosomaisis, most of the endogenous toxic compounds can be conjugated with glutathione via glutathione S-transferase. Therefore, the present study showed the effect of Schistosoma mansoni after 20, 30, 45, 60, and 75 days post-infection on the activity of glutathione-S-transferase (GST) and glutathione reductase (GR), and on the levels of glutathione [GSH] in the livers of male mice. In addition, anti-schistosomal drug (praziquantel) was administered orally [60 mg/kg body weight] for three consecutive days before decapitation of the infected mice at each time point. In the present, depletion of GSH levels was observed at 45, 60 and 75 days post-infection. However, treatment of infected mice at 45, 60, and 75 days post-infection with praziquantel for three consecutive days before decapitation at each time point restored the increased GSH levels to their normal values compared with control groups. Inhibition of GST and induction of GR activities in the livers of S. mansoni-infected mice at all time-points were restored to their normal levels after praziquantel treatment. It is concluded that S. mansoni infection changed the activities of GST, GR and GSH levels. Moreover, it has been found that praziquantel treatment of S. mansoni-infected mice restored such alterations to their normal values and this recovery could alleviate the deleterious effects of S. mansoni infection. In addition, the present study could provide new evidence to the damage occurred in livers of S. mansoni-infected hosts. Also, it is suggested that praziquantel is the best drug of choice for schistosoma mansoni treatment.