The present work evaluates the molluscicidal activities of certain plant extracts (water suspension, Cold water, Boiled water, methanol, ethanol, acetone and chloroform extract). The data obtained from preliminary screening tests conducted on 10 plant species belonging to 10 different families. The effect of low concentrations of different synthetic and natural mollusciciding agents may introduce to fresh water environment on reproduction and biochemical aspects of Biomphalaria alexandrina was studied. Different mollusciciding agents (copper sulphate, Bayluscide, Uccmaluscide, Agave franzosinii, Agave filifera & Agava attenuate). The present study was planned to assess the susceptibility of some naturally associated snails to the molluscicidal activity of monoterpenes in order to evaluate the possibility of applying both chemical and biological methods to control Bulinus truncatus populations. The molluscicidal effect of three monoterpenes (Eugenol, Llinalool and Thymol ) against freshwater snails and the impact of two concentrations of thymol on some enzymatic activity of five snail species naturally associated with Bulinus truncatus.