Schistosomiasis remains a public health problem in many developing countries including Egypt. The disease control initiatives stress on control of snail intermediate hosts side by side with the treatment of infected human cases. Blocking the parasite transformation within the snails will interrupt schistosomiasis transmission. Thus, the present study assessed the antioxidant efficacy of Lanistes carinatus tissue extracts and its role as an immunostimulant for Biomphalaria alexandrina against infection with Schistosoma mansoni. L. carinatus soft tissues were extracted with methanol and the resulting crude extract was further fractioned with petroleum ether, methylene chloride, and ethyl acetate (EtOAc). The total antioxidant capacity (TAC) and total phenolic content (TPC) of all extracts were determined. Furthermore, the effect of the highest antioxidant extract on hemocytes activity (phagocytosis), antioxidant parameters, and infection rate of B. alexandrina was assessed. The results showed that EtOAc extract had the highest antioxidant capacity and total phenolic contents. EtOAc extract led to activation of the phagocytic process with a significant increase in the phagocytic indexes of hemocytes after 1, 2, and 4 h of exposure. In addition, it increased the levels of total antioxidant capacity, superoxide dismutase, reduced glutathione, and glutathione-s-transferase in B. alexandrina compared to controls. The infection rate of snails was significantly reduced due to EtOAc extract exposure. These results collectively suggest that EtOAc extract from L. carinatus has an antioxidant capacity and immuostimulatory effect for B. alexandrina infectied with S. mansoni.