A Maltese was presented with a subcutaneous mass at right flank, depression and hyperthermia. Ultrasonography revealed a hypoechoic mass with hyperechoic foci, a defect of abdominal wall and peritonitis. In cytology, fat necrosis was found. This dog was diagnosed as chronic suppurative steatitis secondary to pancreatitis and pancreatic herniation through surgery and histopathologic examination. Steatitis is recurrent inflammation and necrosis of adipose tissue. Also steatitis associated with pancreatic diseases such as pancreatitis and pancreatic tumor was reported and direct fat necrosis by pancreatic enzyme was supposed as the etiology. Steatitis secondary to pancreatitis was rarely reported in dogs and there was difficulty in diagnosis and treatment. This case has a limitation that pancreatitis was not diagnosed as underlying cause to steatitis before surgery. However, a defect of abdominal wall and peritonitis were observed on ultrasonography. Good prognosis could be achieved through prompt surgery and medical treatment.