The effect of Moringa oleifera seed on the reproductive system of male wister albino rats was studied. Fifteen adult male rats were randomly divided into three groups viz: Test, Control and Baseline. The animals in the baseline group were sacrificed at the onset of the study to determine the initial levels of each andrological parameter. The control group were placed on a compounded diet while the test group received a diet comprising of 1% M. oleifera seed. Data on body weight, testes weight, sperm count (SC), sperm motility(SM), sperm morphology (SMO), and levels of serum testosterone (TT), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were obtained. The initial and final weights for the test, control and baseline were 124.27g (195.02g), 124.87g (169.93g) and 124.79g (0.00g) respectively. The test group showed a significant increase (P=0.05) in body weight as compared to the control and baseline, and also a significant decrease (P< 0.05) in sperm count, sperm motility and sperm morphology; 1.60*109ml, 10.40% and16.40% when compared to the values obtained for the control and baseline which were 22.60*109ml, 62.00%,68.00% and 18.60 *109ml, 54.00%, 64.00% respectively. There was no significant decrease (p>0.05) in the testes weight of the test group compared to the control. There was a reduction in the testosterone level of the test group compared to the control and baseline groups though this was not statistically significant (p = 0.05) .The reduction in the serum luteinizing hormone level of the test and control groups was not statistically significant (p>0.05) compared to the baseline group. There was an increase in the FSH level of the test and control groups in relation to the baseline group though this was not statistically significant (p = 0.05). It can be concluded that M. oleifera seed may have adverse effect on male reproductive system.