Mammary tumors are the most common diseases of canine mammary gland and most frequent neoplasms both benign and malignant, in female dogs. However, mammary gland enlargement and changes may be related to a wide variety of other pathologies. Thus the differential diagnosis should be performed carefully in order to institute an adequate treatment. In this article chosen nonneoplastic disorders like mastitis, hyperplastic and dysplastic changes in canine mammary gland were described.