This invention provides an antitumor agent comprising a combination drug containing tegafur, gimeracil, and oteracil potassium, characterized by being repeatedly administered to a patient once a day every other day, four days a week, at a dose such that the tegafur is administered in an amount of 80 mg or more/dose when the patient has a body surface area of less than 1.25 m2, in an amount of 100 mg or more/dose when the patient has a body surface area of 1.25 to 1.5 m2, or in an amount of 120 mg or more/dose when the patient has a body surface area of not less than 1.5 m2.
