Provided is a novel combination therapy using an FTD/TPI combination drug which exhibits remarkable antitumor effects, and few side effects. This antitumor agent is characterized in that the FTD/TPI combination drug is administered, using a reduced amount of FTD, at a dosage in the range 35-70 mg/m2/day, and CPT-11 is administered at a dosage in the range 45-144 mg/m2/day.本發明提供一種顯示顯著之抗腫瘤效果,且副作用較少之FTD.TPI調配劑之新穎之併用療法。本發明之抗腫瘤劑之特徵在於:以FTD換算量計投予FTD.TPI調配劑35~70mg/m2/天,且投予CPT-11 45~144mg/m2/天。