Inflammatory mammary carcinoma (IMC) is a rare and aggressive type of malignant mammary tumour. An 11-year-old intact male non-descript dog was presented to Madras Veterinary College Teaching Hospital with the history of painful swelling on the ventral abdomen for the past one week. Clinical examination revealed dehydration, sunken eyeballs, unilateral hindlimb edema and pain on palpation. Hematobiochemical studies revealed increase in serum alkaline phosphatase, blood urea nitrogen and creatinine levels. Cytological examination of fine needle aspirate biopsy revealed numerous lymphocytes and erythrocytes with small clusters of atypical cells with anisokaryosis with abundant cytoplasm. The dog collapsed during the treatment and the carcass was submitted to the Department of Veterinary Pathology for necropsy. Detailed necropsy examination revealed exophytic well-circumscribed, firm, red black mass measuring around 7×5×4 cm sized focally on the left cranial thoracic mammary gland. Upon incision, the mass was filled with black clotted blood. On removal of clots, the tumour tissue appeared as pink and multinodular. Histologically the tumour was highly infiltrative and revealed well differentiated cystic papillary mammary adenocarcinoma with osteogenic metaplasia and minimal stromal invasion. Extensive hemorrhages with moderate inflammatory response were also noticed. Immunohistochemical investigations showed immunopositivity for proliferating cell nuclear antigen (PCNA), ki-67, cyclooxygenase 2 (COX-2), cytokeratin and human epidermal growth factor receptor 2 (HER2).