Abstract: The objectives of this study is to investigate the toxic effects of Ballota undulata (300 mg kg-1 b.wt.) on the reproductive system after administration to female Sprague-Dawley rats for two time periods 4 and 12 weeks. Forty adult female Sprague-Dawley rats were divided into two treatment and two control groups of 10 rats each. The two treated groups received 15 mg kg-1 b.wt. of Ballota undulata for two periods of 4 and 12 weeks. Female rats were allowed mating with males after treatment. Several pregnancy parameters were investigated including: total number of pregnant rats, body weight and reproductive organ weight, number of implantation sites, number of resorption sites and number of viable fetuses. The significance of these results was calculated using student's t and Chi-square tests. Exposure to Ballota undulata for 4 weeks did not have significant effects on most parameters investigated. However, a slight decrease in the relative ovarian and embryo weights was observed. Administration of Ballota undulata for 12 weeks significantly reduced the percentage of pregnancies and the number of implantation sites when compared with controls. In addition, a decrease in ovarian weights and in viable fetuses` number was also observed. Histological sections of ovaries of female treated with Ballota undulata were found to have congested blood vessels in cortical and medullary regions. We also noted the arrestment of developing follicles at primary and secondary stages in addition to presence of degenerative areas and hypercellullarity in medulla. Long term treatment with Ballota undulata might lead to diversified negative effects on fertility and pregnancy in female rats.