This study was carried out to detect the differences in some physiological aspects of female reproductive system of Muscovy, Pekin ducks and their intergeneric Hybrid cross. Fifty days old female ducklings from each breed and cross were raised until 25 weeks of age. Ovary, oviduct weights and oviduct length, histological measurements of the ovary and serum progesterone and estradiol concentrations were measured at 4, 8, 12, 16 and 22 weeks of age. The results indicated that there were significant differences between breeds in the studied physiological aspects of the female reproductive system. Crossing between Muscovy males and Pekin females produced intergeneric sterile birds which are known as mule ducks. All characteristic studies of the female reproductive system of these Hybrid ducks were physiologically and histologically abnormal as compared to Muscovy or Pekin ducks.