Present study was undertaken to evaluate the reversible anti-fertility effect of Ocimum sanctum Linn (Tulsi) on male mice. Aqueous leaf extract of Ocimum sanctum was orally administered (0.1ml) for 10 (P < 0.05), 20 (P < 0.01), 30 (P < 0.001), 40 (P < 0.001) and 50 (P < 0.001) days of exposure. Treatment of aqueous leaf extract of Ocimum sanctum showed significant decrease in sperm counts during 10 (P<0.1), 20 (P<0.01), 30 (P<0.01), 40 (P<0.001) and 50 (P<0.001) days treatment than the control. Motility of spermatozoa also declined significantly in treated group after 10 (P<0.01), 20 (P<0.01), 30 (P<0.001) 40 (P<0.001) and 50 (P<0.001) days treatment than the control. However, abnormality of spermatozoa increased significantly in treated group of mice during 10 (P<0.01), 20 (P<0.01), 30 (P<0.001) 40 (P<0.001) and 50 (P<0.001) days treatment than the control. Thus significant decrease in sperm counts, motility and increased abnormality of spermatozoa altered the seminal quality which caused infertility among treated group of mice. Effect of the treatment on reproductive organs and fertility was also investigated. The results revealed that Ocimum treatment caused decrease in the weight of reproductive organs viz., testis (P<0.001), epididymis (P<0.01), seminal vesicle (P<0.001), vas deferens (P<0.01) and ventral prostate (P<0.001) significantly when compared to the control group. The recovery group of animal, which also received 50 days treatment, was maintained for 90 days without any treatment to check the reversibility. All the animals after the recovery period showed normal fertility rate. Thus Ocimum sanctum adversely affects fertility in mice and showed anti-fertility effect among them. From this we can conclude that Ocimum sanctum can be used as a potent anti-fertility agent which is reversible. Key-wordsOcimum sanctum, Anti-fertility, Sperm count, Motility, Sperm abnormality -------------------------------------------------IJLSSR----------------------------------------------INTRODUCTION One of the important concerns today’s is the problem of over population. If the population increase is not controlled or checked, it will lead to several problems (Sailani and Moeini, 2008). The solution to this predicament is population control. India opted for family planning to control the increase in population (Sarkar, 1996). Various methods of contraception were used for fertility control. There are a variety of methods available and are in use for female contraception (Bajaj, 1999). In contrast, except for the barrier method and vasectomy, there are no methods available for male contraception. Thus, there is need to develop multiple male contraceptive methods. The risk obtained by the drugs has triggered the need to develop newer molecules from medicinal plants. Access this article online Quick Response Code: Website: www.ijlssr.com