Abstract: This study was conducted to screen different snail species to determine their susceptibility for different parasitic infections and also to determine LC50 and LC90 values. The screening of snail species infected with Schistosome parasite and mean number of cercariae shed by individual infected snail was 184±12. The experiment on relationship of snail size and dose of Niclosamide showed that juvenile snails were more susceptible to chemical when compared with adult snails. A series of seven experiments indicated that concentration of 0.067 and 0.109 mg L-1 were required to kill 50 and 90% snails, respectively in an exposure period of 24 h and no death occurred in recovery period.