We report a case of a 35-year-old patient with acute pancreatitis after administration of ceftriaxone. She was given ceftriaxone (2g/day) for 9 days because of diverticulitis of the colon. She was admitted to our hospital again because of epigastralgia 12 days after the first administration of ceftriaxone. Laboratory examination showed markedly elevated serum amylase, and CT scan demonstrated findings consistent with acute pancreatitis, in addition to sludge in the common bile duct and gall bladder, which was not identified before the administration of ceftriaxone. We should be aware of the fact that administration of ceftriaxone sometimes results in the formation of biliary sludge and can cause severe adverse events such as cholecystitis and pancreatitis, not only in children, but also in adult patients.