We evaluated the effect of Kampo therapy in which Kampo formulae were selected based on Japanese traditional theory, on the development of hepatocellular carcinoma (HCC) in patients with hepatitis C virus (HCV)-related chronic liver disease. One hundred forty HCV-infected outpatients without HCC at their first examination and who were observed for more than one year, were included. The patients were divided into three groups according to the initial platelet count (Plt): Plt less than 10×104/μL (Group I), Plt between 10×104/μL and 14×104/μL (Group II), and Pit greater than 14×104/μL (Group III). For each patient, Kampo formulae were selected according to the patient's symptoms and physical findings at each clinic visit. The incidence of HCC calculated by the person-years method, was 0.89% in Group I. 1.55% in Group II and 0.29% in Group III. The annual incidence of HCC among our patients was low compared with that among untreated patients in previous reports. In addition, the incidence of HCC among our patients was low compared with that of previous studies where Shosaikoto or Juzentaihoto was administered for a long period of time. In the present study, age over 60 years was a possible risk factor for HCC. However, sex and patterns of the change in alanine aminotransferase level (ALT) were not associated with the development of HCC. A total of 53 different Kampo formulae were prescribed, for all patients, with Hochuekkito being the most frequent. These results suggest that Kampo treatment in which Kampo formulae are selected based on traditional theory, may be more useful than treatment by a single Kampo formula for preventing the development of HCC in patients with HCV-related chronic liver disease.