The effect of exposing B. alexandrina to sub-lethal dose (LC10 & LC20) of Myrrh, on its susceptibility to infection with S. mansoni miracidia were determined. Starting three weeks post miracidial exposure, cercarial shedding was monitored. No shedding of cercariae were observed from snails treated with LC20. In snails treated with LC10, longer prepatent cercarial and shorter cercarial production periods than those of control group were recorded. The number of infected snails and of shedding cercariae were decreased. The study revealed that sublethal values of myrrh decreased the compatibility of B. alexandrina to S. mansoni infection thus playing an important role in the control of schistosomiasis.