Objective: Carrot (Daucus carota L.) is known to possess antifertility properties in female. However, according to Iranian traditional medicine, it can increase the potency in men. The aim of this study was to investigate the influence of carrot seed extract (CSE) on spermatogenesis, number and motility of sperms in cauda epididyme in male rats. Materials and Methods: Forty adult male rats were randomly divided into 5 groups: control group, groups receiving low- and high doses of CSE, animals that received high-dose of CSE with gentamicin, and a gentamicin only group. After 4 weeks treatment, fasting serum samples were obtained for the sex hormone analysis. Under anesthesia, testis, cauda epididymides and sperm ducts were dissected and sperm count, motility and cauda epididymis sperm reserves (CESR) were determined. Histopathological changes of testis were also studied to assess spermatogenesis. Data analysis was performed using one-way ANOVA followed by Tukey HSD tests. Results: Administration of CSE caused a significant increase in CESR compared with the control (28.2 ± 1.8 vs. 45.1 ± 2.0, ×106). The extract could also protect testis from the gentamicin- induced necrosis. The CSE administration caused about 3.5-times increase in the LH levels even in spite of receiving 5 mg/kg/day gentamicin with no significant effect on FSH levels. The testosterone concentrations in the group received 400 mg/kg CSE were 30% and 83% higher than its levels in the control and the gentamicin treated group, respectively. Conclusion: CSE can overcome reproductive toxicity of gentamicin and induces spermatogenesis probably mainly through the elevation of testosterone levels. It appears that this extract has opposite effects on male and female reproductive systems.