A 2-year-old male mixed breed dog was presented with history of a slow growing subcutaneous mass on the back near to left hip joint. Grossly, a large, firm, gray-white mass about 4.5 × 3.5 × 7.5 cm in dimensions was located within the dermis. Microscopically, a poorly encapsulated, multilobular tumoral tissue was observed with proliferation of the glandular epithelium as tubular and solid structures. The proliferating epithelial cells lining the tubules had round to ovoid, normochromatic nuclei with prominent nucleoli and relatively large eosinophilic cytoplasm. The lumens of a number of tumoral tubules were distended by eosinophilic secretions as hyaline casts. In immunohistochemistry, immunoreactivity for the S-100 protein and cytokeratin were diffusely and randomly positive, respectively, and for P63 was negative in the neoplastic cells. On the basis of the gross and histopathological findings, the tumor was diagnosed as apocrine sweat gland adenocarcinoma.