Aim: To investigate the effect of Morinda lucida Benth (Rubiaceae) on the reproductive activity of male albino rats. Methods: Two groups of rats were treated with 400 mg/(kg·d) of Morinda lucida leaf extract for 4 and 13 weeks, respectively. The control rats received the vehicle. All the treated rats had corresponding recovery groups. At the end of each experimental period, animals were killed and organ weights, sperm characteristics, serum testosterone levels, histology of the testes and fertility were assessed. Results: Morinda lucida leaf extract did not cause any changes in body and somatic organ weights, but significantly increased the testis weight (P < 0.05). The sperm motility and viability, and the epididymal sperm counts of rats treated for 13 weeks were significantly reduced (P < 0.05). Sperm morphological abnormalities and serum testosterone levels were significantly increased (P < 0.05). There were various degrees of damage to the seminiferous tubules. The extract reduced the fertility of the treated rats by reducing the litter size. Reversal of these changes, however, occurred after a period of time. Conclusion: The extract of Morinda lucida has reversible antispermatogenic properties. (Asian J Androl 2005 Dec; 7: 405–410)