Acute pancreatitis and afferent loop syndrome (ALS) have similar symptoms and physical findings. Accurate early diagnosis is essential, as the management of acute pancreatitis is predominantly conservative whereas ALS usually requires surgery. We experienced one case of pancreatitis due to ALS with internal hernia. Laboratory findings of patient showed elevated serum amylase, lipase and WBC count. One day after admission, diagnosis was modified as acute pancreatitis caused by ALS on computed tomography. Patient was managed with surgical treatment and operation finding revealed ALS due to internal hernia. He was recovered well after surgical treatment and discharged without significant sequelae.