A case of primary adenosquamous carcinoma of the liver with an elevated level of serum squamous cell carcinoma related antigen is herein reported. Various hypotheses on the pathogenesis of adenosquamous carcinoma of the liver have been set forth previously, however there is still no widely accepted theory because of the absence of any sufficient evidence. The postoperative transition of serum squamous cell carcinoma related antigen and the immunohistochemical findings using anti-involucrin antigen in this case support the hypothesis that the squamous cell carcinoma component arises as a result of the metaplastic transformation of adenocarcinoma cells.