Introduction: Fetal programming hypothesis presupposes that stimulus or insult acting during critical periods of uterine growth and development do alter tissue structure and function. In the present study changes in histomorphometric integrity of the testes and epididymis in adult F1 male rats maternally exposed to Ricinus communis oil (RCO) at different gestation periods were assessed. Materials and Methods: Therapeutic dose of RCO 950 mg/kg BW was administered to pregnant Wistar rats at gestation days GD 1-7, 7-14, 14-21 and 1-21 respectively. Testes and epididymis of adult male F1 offspring were then harvested for Histomorphometry assessment under Light microscope. Seminiferous tubular diameter (STD), seminiferous luminal diameter (SLD) and Seminiferous epithelial height (EH) of both peripheral and central seminiferous tubules were measured in the testes. Epididymal tubular diameter (ETD), epididymal luminal diameter (ELD) and epididymal epithelial height (EEH) were measured in epididymis. Results: Results were expressed as the mean ± SEM and significance taken at p<0.05. STD significantly (p<0.001) increased in F1 males from GD1-7, 7-14, 14-21 relative to control group. SEH significantly (p<0.001) decreased in F1 males from GD1-7,7-14 and 1-21. SLD increased significantly (p<0.001) in F1males from GD1-7, 7-14, 14-21 and 1-21. ETD significantly (p<0.01) increased in F1 males from GD1-7, 7-14, 14-21. EEH significantly (p<0.001) increased in F1 males from GD1-7 and GD7-14. ELD however increased significantly (p<0.001) only in F1 males from GD1-7. Conclusion: Maternal RCO exposure at different gestation periods impaired negatively histomorphometry of the testis and epididymis in male offspring.