Abstract: This research was aimed to study the significance of the mixture from the aquatic plant, duck weed and Bacillus thuringensis israelensis as a potent deterrent factor limiting mosquito Culex pipiens populations in the field. C. pipiens mosquito appeared highly sensitivity for the higher concentrations (ppm) of Bacillus thuringensis israelensis (Bti); 100% mortality was recorded in the third and fourth instar larvae after treated by 90 and 9 ppm, respectively. The third and fourth instar larvae were appeared high susceptible to the allelochemicals of duckweed, Lemna minor. Water half covered by duckweed increase the efficacy of Bti. on the third and fourth instar larvae of mosquito.