Pesticide exposure may affect semen quality and male fertility in humans. The aim of the present work was to elucidate the adverse effects of deltamethrin (Delta), a synthetic pyrethroid, on exposed male mice and their offspring. Adult male Albino/Swiss mice received deltamethrin (5 mg/kg) daily for 35 days and mated with untreated females to produce offspring. Classical measurements of ejaculate and sperm quality and testicular histopathological changes were assessed. Deltamethrin treatment affects sperm quality and quantity in the ejaculated semen of mice that had also markedly impaired libido as measured by indices of mating and fertility and number of pregnant females housed with male mice exposed to this pesticide. Exposure mice to deltamethrin significantly decreased their testosterone and inhibin B levels and affected reproductive performance. Testes of exposed mice showed marked histopathological alterations as compared to the control group. The mice exposed to 5 mg/kg body weight/day of deltamethrin showed severe alterations of the seminiferous tubules, sloughing of the germ cells, the vacuolization of germ cell cytoplasm, and the disruption of spermatogenic cells compared to the control group. Altered pregnancy outcomes were directly attributed to damage of sperm of male mice exposed to deltamethrin compared to the control group. We concluded that exposure to deltamethrin affected the reproductive system of male mice explored by altered total sperm density, motility, and morphology in mice spermatozoa.