The fecundity, viability and the size of egg-masses were studied in Physa acuta and Helisoma duryi snails treated with 1 ppm Bayluscide for two hours. Bayluscide application caused significant and highly significant reduction in the fecundity of both Physa acuta and Helisoma duryi. However, an increase in the fecundity was observed for both treated snails in few days after exposure. Moreover, Bayluscide did not lead to stoppage of egg laying at any day of experiment. Bayluscide caused a reduction in the viability of egg-masses produced by treated Physa acuta or Helisoma duryi snails since they produced higher numbers of abnormal eggs containing dead embryo. Moreover, application of 1 ppm Bayluscide for two hours against Physa acuta caused a decrease in the size of egg-masses produced by treated snails. This is expressed by the production of higher percentage of egg-masses containing small numbers of eggs as compared with those masses produced by control snails.