Assessments of the reproductive toxicity of organophosphorus insecticides are important public health issues. The adverse reproductive effects of one of the commonly used organophosphorus members, namely; phosmet on male rats were investigated. The tested insecticide was given orally to male rats at five dosage levels (phosmet, 0.81, 1.62, 3.25, 6.5 and 13 mg kg^-1 b.wt) for 60 consecutive days. Plasma testosterone levels, sex organs weights, semen quality as well as histopathological finding of testis were the criteria used to evaluate the reproductive efficiency of the treated rats. A dose-dependant decrease was observed in the weights of the most genital organs, sperm cell concentrations and sperm motility associated with a significant increase in the percentage of dead morphologically abnormal spermatozoa of treated rats. Plasma testosterone level was declined significantly in phosmet treated groups at 3.25, 6.5 and 13 mg kg^-1 b.wt. Sperm cell concentrations was severely affected by phosmet at high dose level (3.25, 6.5 and 13 mg kg^-1 b.wt,). Histopathological examination of the testes revealed a mild, moderate and severe histopathological changes in rats treated with phosmet and severity was dose dependent. It is concluded that, phosmet induced adverse effects on male rats fertility by impairing both testicular function and structure.