In this research, 30 canine mammary tumor tissues which were diagnosed as tubulopapillary carcinoma and complex carcinoma were used. The routine avidin-biotin-peroxidase complex method (ABC) was applied for detection of Nectin-4, Proliferating Cell Nuclear Antigen (PCNA) and Ki-67 in these tissues. The results were analyzed comparatively and evaluated semi-quantitatively. Immunohistochemically, Nectin-4 was expressed in the plasma membrane and cytoplasm of malignant tumor cells. Statistically, positive, linear and a high correlation was observed between Nectin-4, PCNA and Ki-67 expressions. For this reason, it has been concluded that Nectin-4 may be of significant prognostic value relating to malignancy in canine mammary carcinomas.