The seeds of Nigella sativa Linn. (Ranunculaceae) are commonly known as black seed or black cumin and locally called as kalonji. The seeds of Nigella sativa are used in herbal medicine all over the world for the treatment and prevention of a number of diseases and conditions. The present study revealed that oral administration of black seed (Nigella sativa) oil at a dose rate of 5ml/kg body weight for 60 days on daily basis had positive effect on spermatogenic activity in terms of histomorphometrical characteristics of testes i.e., diameter and area of seminiferouse tubules, percentage area of interstitial cells in relation to seminiferouse tubules, spermatogenic cell layer of seminiferouse tubules, thickness of germinal layer and volume of seminiferouse tubules of testes of all rabbits. Number of spermatogonia and serum testosterone concentration also increased in treated group as compared with the control group. Thymoquinone might be the major component of black seed (Nigella sativa) oil important for enhanced testicular activity.