The present study is a trial to investigate the toxic effects of the bio-pesticide Bacillus thuringiensis (Bt) on male reproductive system of rats. Rats received dietary doses each approximately equivalent to 1/10 or 1/100 of the LD50 value of the Bt bio-pesticide (Agerin) for 90 consecutive days. Sex organs weight, semen picture, concentrations of the hormones [i.e., testosterone, luteinizing hormone (LH), and follicle stimulating hormone (FSH)], and histopathological changes in testes were the criteria used to evaluate the reproductive toxicity on the treated rats. Btat the higher dose caused a significant decrease in the weight of testes and seminal vesicles as compared with control. Both Bt doses decreased sperm count associated with an increase in the morphologically abnormal spermatozoa; however sperm motility was significantly decreased in treated rats with the higher dose only. The concentration of serum testosterone was significantly reduced in both treated groups; however LH and FSH levels were significantly reduced in treated rats with the higher dose. Histopathological examination of Agerin-treated male rat's testes revealed that both Bt doses caused testicular degeneration in a dose-dependent manner. In conclusion, Agerin may decreases fertility in adult male rats by affecting the concentrations of pituitary gonadotrophins, testosterone and thus subsequent spermatogenic impairment