The joint action of the binary mixtures of chlorpyrifos (organophosphorus) or beta-cyfluthrin (pyrethroid) plus three chitin synthesis inhibitors(flufenoxuron, chlorfluazuron and lufenuron) on the 4^th instar larvae of the laboratory strain of the cotton leafworm Spodoptera littoralis (Boisd.) at LC₂₅ level were evaluated. In general, according to co-toxicity factor data clearly indicated that all tested mixtures decreased the toxicity except for the combination between chlorpyrifos and lufenuron, it produced additive effect (-19.15). The tested mixtures of Beta-cyfluthrin with all tested insect growth regulators (IGRs) were high antagonism (ranging between - 55.56 and - 84.13) than the tested mixtures of IGRs with chlorpyrifos. The effect of both tested individual insecticides and it's mixtures on the activity of esterases (α- & β-esterase), transaminase (AST and ALT) chitinase, alkaline phosphatase, total proteins, total lipids and glucose was determined colorimetrically.