Abstract: Histological and morphometric methods were used to study the changes of histology and morphology of yak′s uterus during estrus cycle. The results showed that the wall of yak′s uterus was composed of mucous membrane(endometrium), tunica muscularis(myometrium)and tunica adventitia(perimetrium). The endometrial surface and glandular epithelium were simple columnar epithelium at follicular phase and increased obviously at luteal phase which were pseudostratified columnar epithelium. The endometrial surface epithelium consisted of secretory cells and a few lymphocytes. The secretory cells included light and dark cells. In general, the cytoplasm of the light cells was lighter than that of dark cells, and has a large and columnar shape. The dark one has a laterally compressed and slim shape. The component of the glandular epithelium was similar to that of the surface epithelium. There were abundance of PAS-positive granules in the endometrial surface epithelium, glandular epithelium and stroma were observed with PAS reaction during the luteal phase more than that of the follicular phase. The invaginated(telescoping)gland, enlarged gland and accumulated lymphocytes were occasionally found in the lamina propria during the follicular phase, but during the luteal phase only the telescoping gland was observed in the lamina propria. Furthermore, the thickness of endometrium and myometrium increased significantly at luteal phase, than that of the follicular phase(P＜0.01). The mean gland duct diameter, area, perimeter, total glandular area and perimeter of the endometrial glands were significantly higher at the luteal phases than that at the follicular phase(P＜0.01), but there was no significant change in the number of gland ducts(P>0.05). Therefore, there was a regular change in the histological structure of the yak′s uterus during the estrus cycle.