Gastrectomy is commonly performed for both benign and malignant lesions. Although the incidence of post-gastrectomy acute pancreatitis (PGAP) is low compared to other well-recognized post-operative complications, it has been reported to be associated with a high mortality rate. In this article, we describe a 70-year-old man with asymptomatic pancreatic divisum who underwent palliative subtotal gastrectomy for an advanced gastric cancer with liver metastasis. His postoperative course was complicated by acute pancreatitis and intra-abdominal sepsis. The patient eventually succumbed to multiple organ failure despite surgical debridement and drainage, together with aggressive antibiotic therapy and nutritional support. For patients with pancreas divisum or dominant duct of Santorini who fail to follow the normal post-operative course after gastrectomy, clinicians should be alert to the possibility of PGAP as one of the potential diagnoses. Early detection and aggressive treatment of PGAP might improve the prognosis.