Third larval instars of Culex pipiens were exposed to sub-lethal concentration LC₂₅ of Black and White liquors (waste extract from rice straw) for 24 hours to study its effect on protein content quantitative and qualitative. The total protein contents in larval treated either with black liquor or with white liquor were high in all developmental stages except in pupal stage Black liquor treatment was low but not significantly as compared to the control insect. The protein profile of the treated larvae and other developmental stages (pupa, adult female and adult male) was evaluated to explain their mode of action. Electrophoretic analysis of total proteins revealed inhibitory action of the tested compounds on the protein contents. The appearance and disappearance of certain protein fractions by application of these compounds may be explain their larvicidal activity and disorders occurred during different developmental stages.