Abstract: In this study search for LC50 concentration thiourea and nickel chloride (cancerogen) on Acanthodiaptomus denticornis and Cyclops vicius (Copepoda) have been investigated. A solution in different concentration has been put into an environment of, 15 cc containing 10 individual and by observing for 24 h, the death rate has been investigated and by using the control group, 15 sperate test have been made for each different test and by having the varage number of them, the death rate in each concentration has been calculated. As a result the LC50 concentration has been determined.