The association between acute pancreatitis (AP) and gastrointestinal cancers in diabetic patients is currently not well understood. The study aim was to investigate the association between AP and gastrointestinal cancers in diabetic patients. Data from the Korean National Health Insurance Service database were analyzed. Participants with diabetes who underwent a health examination between 2009 and 2012 were followed up till December 2018. The primary outcome was the occurrence of gastrointestinal cancer. A total of 2,263,184 patients were included in the final analysis. Patients with a history of AP (n = 2390) were found to have a significantly higher risk of gastrointestinal cancer, except for esophageal cancer, as follows: gastric cancer (aHR = 1.637, 95% CI: 1.323-2.025), colorectal cancer (aHR = 2.183, 95% CI: 1.899-2.51), liver cancer (aHR = 2.216, 95% CI: 1.874-2.621), pancreatic cancer (aHR = 4.558, 95% CI: 4.078-5.095), bile duct cancer (aHR = 3.996, 95% CI: 3.091-5.269), and gallbladder cancer (aHR = 2.445, 95% CI: 1.459-4.099). The history of AP is associated with the increased risk of gastrointestinal cancer in diabetic patients. It is necessary to investigate the history of AP and more actively recommend screening for gastrointestinal cancers in such patients.