A rare disease characterized by painless jaundice, autoimmune pancreatitis could mimic pancreatic cancer with the presence of pancreatic head tumor. The disease responds well to steroids, and early diagnosis can avoid unnecessary surgery and complications caused by recurrent inflammation of the pancreas. The patient was a 68-year-old man receiving examination and treatment at our gastroenterology department for persistent abnormal results for liver function tests, swollen pancreas, a pancreatic head tumor, and obstructive jaundice after allergic reaction caused by Vaxzevria (AstraZeneca) COVID-19 vaccination. Autoimmune pancreatitis was diagnosed after image examination and laboratory and pathology tests. The patient recovered well after treatment with steroids. The abnormality previously noted returned to complete normality. In conclusion, when physicians encounter a patient with painless jaundice and pancreatic lesions, autoimmune pancreatitis, although uncommon, should be considered for differential diagnoses.