Patients with immunoglobulin (Ig) G4-related sclerosing cholangitis typically have a high serum IgG4 level. However, here we describe our experience of a patient with a normal serum IgG4 level for whom the cholangitis was diagnosed by liver biopsy. A 61-year-old male presented with elevated liver enzymes and a normal serum IgG4 level. The hilar, intrahepatic, and upper extrahepatic bile ducts were stenotic, with no evidence of a pancreatic lesion. We therefore performed a liver biopsy to differentiate between cholangiocarcinoma and primary sclerosing cholangitis. Pathological examination revealed lymphoplasmacytic infiltrates around the bile ducts with a storiform fibrosis. IgG4-positive plasma cells were also observed. These results fulfilled the Japanese diagnostic criteria for IgG4-related sclerosing cholangitis. When this condition is suspected, liver biopsy should be performed even when serum IgG4 levels are normal.