A 12 years old female German Shepherd dog was presented to Veterinary Hospital with a history of vomiting, distended abdomen and the presence of fluid in the abdominal cavity. Abdominal fluid was pink/white in colour with opaque clarity and too lipemic that made difficult to estimate total protein. Value of triglyceride in the fluid was 438 mg/dl. Numerous clusters of cohesive cells in variable size amid many leukocytes and blood were observed in the smear slides which were made from the sediment of the fluid. Occasionally, cohesive cells were formed as an acinar-like structure around eosinophilic materials (collagen core). Cells were ovoid to polygonal with a round to ovoid nucleus, coarse chromatin, one to four variably sized nucleoli and a moderate to abundant volume of basophilic to deeply basophilic cytoplasm. A variable number of clear, round cytoplasmic vacuoles were observed in some cells. Moderate anisocytosis and anisokarosis, bi-and multi nucleation and prominent multiple nucleoli were observed in some cells. Some cells showed window interdigitating microvilli. These findings are consistent with a malignant mesothelioma.