Laboratory experiment was conducted to examine sublethal effects of beta-cyfluthrin (Bulldock^® 025 SC) on the sepia mutant of Drosophila melanogaster at a temperature of 25±0.5°C, 50±5% relative humidity and a photoperiod of 16 : 8 (light : dark) hours. Males and females were exposed separately to beta-cyfluthrin (one tenth of the calculated LC₅₀ value) mixed in the diet for 24, 48 and 72 h. Fecundity, hatchability, pupation, adult emergence, larval, pupal and total developmental periods were evaluated in the F₁ generation after various cross combinations. A reduction in fecundity, egg hatching, number of larvae, pupae, adults and prolongation of larval, pupal and total developmental periods was observed. A significant reduction (p<0.05) in fecundity was observed only on the treated diet after treatment of both the sexes. Maximum effects were observed after 72 h treatment followed by 48 and 24 h. Males were found to be more susceptible to beta-cyfluthrin as compared to the females.