Abstract: The aim of this study was to reveal the tissue structure and the distribution and number changes of abomasum mucosal immunityassociated cells in the yak. The tissue structure and intraepithelial lymphocytes, plasma cells and mast cells of abomasum in the yak were investigated with histochemical method, the scion image software analysis techniques method and the electron microscope technique. The results showed that there were mucousmembrane, submucosa, tunica muscularis and serosa in the abomasum of yak. The gastric pit was deepest in the pyloric gland region of abomasum, and this glandular region has also the longest gland and the thickest muscular layer. The thickness of muscular and glands length in each glandular region of abomasum are significantly different (P<0.01). The gastric pit of the pylorus gland region is significantly different (P<0.01) with the fundus gland region, and it has also significantly difference compared with the cardiac gland region, but the gastric pit of the fundus gland region is quite similar (P>0.05) to the cardiac gland region. The number of intraepithelial lymphocyte and plasma cell in each glandular region of abomasum are not significantly different（P>0.05). The number of the mast cells between the fundus gland region and the pyloric gland region are significantly different (P<0.01), the fundus gland region has most mast cells, and the pyloric gland region has the lest mast cells, but both of them are similar to the cardia gland region (P>0.05). There are a lot of diffuse lymphatic cells and solitary lymphoid nodules in the lamina propria of abomasum. Under the electron microscope, gastric pit columnar epithelial cells are aligned tightly. There are lots of mucous cells in the lamina propria of pylorus gland region, these cells are tall columnar or cone shape, their nucleus are located basally part of the cell, there are the high electrons density particles are gathered in the top of these cells. There are a large number of parietal cells and chief cells in the fundus gland region and cardiac gland region. The structure of abomasum in the yak is similar to other ruminant animals, but each layer has its characteristics. There are quite a lot of diffuse lymphatic cells and solitary lymphoid nodules in the lamina propria of abomasum in the yak, it make the abomasum mucosal immunity function of the yak stronger than other ruminant animals.