A 74-year-old male was diagnosed with transverse colon carcinoma with idiopathic mesenteric phlebosclerosis (IMP). Extended right hemicolectomy with regional lymph node dissection was performed. It has been reported that IMP develops after taking Chinese herbs containing SANSIS for a long time. In this case, the patient had taken such an herb for more than 3 years. In Japan, total 6 cases have been reported on a tumor with IMP, including this case. Immunohistological examination showed that the IMP findings were particularly strong around the tumor. Thus, this case suggests that there is a link between the tumor and IMP.