An 8 year old intact male boxer was diagnosed to be affected with insulinoma. The dog was treated by massectomy. Mass was sent to be confirmed for histopathology. The result showed as islet cell tumor. Post-operative management displayed the increased in pancreatic profiles; Lipase, Amylase and cTLI. The increased profiles can decreased to the normal level within 48 hours. However, the surgical complication presented as peritonitis which corrected by two peritoneal larvages. During the peritoneal larvage the perforated caecal mass and ileum were detected, so that massectomy and end-to-end anastomosis was performed. Chronic pyogranulomatous ileitis was histopathological diagnosed. In conclusion peritonitis was post-operative complication results from acute pancreatitis concurrent with caecal mass perforation. Hence pancreatic surgical procedure has to be operated with gentle tissue handling to minimize the post-operative complication.