ObjectiveTo compare the uterine and ovarian morphologies between diestrus and estrus Beagles for the further study of their reproductive inefficiency.Methods Detected the serum sexual hormone of 23 Beagle bitches, which have been produced once or twice, using chemiluminescence and selected 2 estrus and 4 diestrus Beagles by serological identification for ovarian and uterine specimens, 4% neutral paraformaldehyde-fixed, paraffin-embedded, routine HE stained, photographed. ResultsThe uterus and endometrium of diestrous dogs are thin, interstitial fibrosis, corpus luteum are occupied by primary follicles, 1-2 visible secondary follicles, no mature follicles. Follicular and luteal cells have more fiber, less vascularized. While the uterus and endometrium of estrus Canines are more thicken, endometrial cavity is larger, part of the gland is branched bend, glandular cells are enlarged, cytoplasm pale dyed, with a small number of visible vacuoles under the nuclear. Ovarian follicles are in large numbers, and are mainly primary, secondary and 1-2 mature follicles. There are numeric luteal cells which arranged regulatory, state clearly, loose interstitial fibrosis, vascular, and no vacuolar degeneration. Diestrus and estrus dogs’ ovarian have no obvious white body. Conclusion Diestrous Beagle sex hormone is maintained at a relatively low level, in proestrus estrogen levels increased rapidly, and after ovulation progesterone levels were higher. Morphological changes of ovary and uterus are adapted to the estrous cycle of bitches.