Echinostoma liei (Jeyarasasingam, Heyneman, Lim and Mansour, 1972), was used for the first time as bio control agent for the wild rat Rattus rattus frugivorus Rafinesque. Two levels of infection were used (250 and 500 metacercariae / rat) and histopathological alterations were studied in the affected organs (intestine ,liver and testis). The investigation revealed that high infection of E. liei resulted in severe pathological alteration in rat intestine, and liver, such as edema, lymphocytic infiltration, necrosis and hemorrhage in the liver lead to death in addition to testis hypertrophy with seminiferous tubules devoid of sperms that may lead to sterility. Thus, E. liei could be considered a new effective biological agent for controlling wild rats causing either death or sterility and also safe to human since people in Egypt don't eat fresh water snails either raw or cocked).