Callosobruchus maculatus is the major insect pests in Nigeria that causes significant loss by damaging stored cowpea seeds thereby reducing their market value and nutritional quality. A study was conducted to investigate the insecticidal potency of sesame (Sesamum indicum L.) leaf powders in protecting cowpea seeds against cowpea bruchids’ infestation. The adult insects were introduced into plastic containers containing cowpea seeds treated at four different concentrations of sesame leaf powder (2.0, 4.0, 6.0, 8.0g each per 20g of cowpea, respectively) while Ampligo insecticide treated seeds and untreated seeds were used as positive and negative controls, respectively. The experiment was laid out in a Completely Randomized Design with three replications and left for a period of three months. Data obtained were analysed using Analysis of Variance, with Duncan’s New Multiple Range Test to separate significant means. The result obtained revealed significant difference (P?0.05) in the efficacy of the powders in protecting cowpea seeds against the pest. The result showed that 8.0 g of the powders exerts more than 50% mortality to the test insects and inhibit oviposition to as high as 91.18%. The powders offered comparable protection of treated cowpea seeds for one to three months with respect to the negative control against C. maculatus. The effect is dose dependent, increases with increase in dose. The insecticidal potency of the powders could be attributed to the active phytochemicals present therein. Therefore, 8.0 g of sesame powder per 20 g of cowpea is recommended as effective biopesticide against stored cowpea bruchids’ infestation.