The present paper deals with the toxicity evaluation of pesticides acephate and chlorpyrifos by applying dominant lethal test (DLT) on mosquito Culex quinquefasciatus taken as an experimental model. For this, the adult male mosquitoes emerging from LC20 treated larval stock were allowed to crossmate with normal virgin females under controlled conditions of mosquito rearing laboratory along with the parallel controls, separately for each pesticide. The eggs obtained from such females were allowed to hatch after which they were examined under suitable magnification. The number of unhatched eggs was taken as the measure for calculating the dominant lethality caused by the pesticides and the data was analyzed statistically by applying Student's t-test. The statistical analysis of the results for acephate treated groups was 9.49 +/- 1.50 as against 3.92 +/- 0.41 in the control groups and chlorpyrifos treated groups gave the value 9.94 +/- 1.92 as against 4.26 +/- 0.35 in the control groups. The results indicated that these pesticides induced significant (p < 0.05) dominant lethality.