Artemether (ART), the methylated derivative of artemisinin, is an efficacious antimalarial drug that also displays antischistosomal properties. This study was designed to evaluate the therapeutic action of single intramuscular dose (50 mg/kg body weight) of ART on S. mansoni infected mice. The parasitological studies showed that maximum effect was reached when ART treatment interfered with 14 or 21 days old schistosomula. This was reported as reduction in worm burden and distribution, female worm fecundity, oogram patturn and tissue ova count. However, ART showed fewer effects on adult worms. Furthermore the immunological studies found that ART treatment at these times also decreased the anti-SEA total IgG, IgG2 and IgG4 levels reflecting a probable protective action against reinfection. On the other hand, ART found to have no effect on serum level of anti-SEA IgM. Furthermore, ART treatment at 14 or 21 post infection demonstrated a stimulatory effect on IFN-¿ combined with a suppressive effect on both IL-4 and IL-10. This Th1 predominant cytokine profile reflects a probable reason for the recorded down modulation of granuloma.