Immunoglobin G4-related sclerosing cholangitis (IgG4-SC) is recognized as one of the systemic sclerosing diseases characterized by abundant IgG4-positive plasma cells with effective steroid therapy. On the other hand, primary sclerosing cholangitis (PSC), recognized as a sclerosing cholangitis of unknown origin without steroid efficacy, has been often clinically confused with IgG4-SC. To date, the prognosis of IgG4-SC is unclear, while the prognosis of PSC is well known to be poor. Therefore, it is clinically very important to be able to distinguish IgG4-SC from PSC. However, at the present time it still remains unclear whether PSC may sometimes be misdiagnosed as IgG4-SC or not. Herein, we report three rare cases of PSC with elevated serum IgG4 levels and/or an infiltration of abundant IgG4-positive plasma cells in the liver: a young male with ulcerative colitis (UC), and elderly female and a young female, each with elevated serum IgG4 levels. The first two patients showed infiltration of abundant IgG4-positive plasma cells in the portal area of the liver without response to steroid therapy. From our experiences, we emphasize that some patients with PSC, who do not respond to steroid therapy, show elevated serum IgG4 levels and/or infiltration of abundant IgG4-positive plasma cells, although the mechanism still remains unclear.