Abstract: The study investigated the effect of melatonin on artificial crytorchidism in Sprague-Dawley rats. Forty rats weighing 220-270 g were divided into five treatment groups A, B, C, D and E with group A as control. The rats were rendered unilaterally (B and D) or bilaterally (C and E) cryptorchid by anchoring the upper pole of the testis to the abdominal wall. Groups D and E in addition received 0.7 mg kg^-1 body weight of melatonin intraperitoneally between 9.00-10.00 am daily for 56 days. The control group gained 40% of their initial body weight while the mean weight losses of the cryptorchids were 27 and 23% (unilateral and bilateral without melatonin) and 45 and 39% (unilateral and bilateral with melatonin). Mean Paired Testes Weight (PTW) of control rats did not differ significantly (p>0.05) from those of groups B and D (unilateral cryptorchids with and without melatonin respectively) and E (bilateral cryptorchid with melatonin) but was significantly higher than the mean PTW of group C (bilateral cryptorchid without melatonin respectively). The ipsilateral testis without melatonin was lower in weight than the contralateral testis (B) while the weights were equal in melatonin treated rats (D). The mean PTW of bilateral cryptorchids with melatonin (E) was higher than the PTW of bilateral cryptorchids without melatonin. There was no sperm cell in the ipsilateral cauda epididymis of group B and the bilateral epididymides of group C rats that did not receive melatonin treatment (azoospermia). The epididymis of groups D and E rats, with melatonin administration had significantly (p<0.05) lower spermatozoa concentration (oligospermia) than the control rats. There was no significant (p>0.05) difference between epididymal sperm concentration and motility of the control rats compared with the contralateral testis of groups B and D rats. Motility of cryptorchid epididymal sperm was slow and non-linear. It was concluded that artificial cryptorchidism negatively affected metabolic activities in male Sprague Dawley rats. The contralateral testes of artificial, unilateral cryptorchids were not significantly (p>0.05) affected by the negative effect of artificial cryptochidism on the ipsilateral testes. Artificial cryptorchidism did not affect blood plasma testosterone level. Melatonin alleviated the deleterious effect of artificial cryptorchidism.