Disclosed are an antitumor preparation comprising a combination of (1) a combination drug of tegafur/gimeracil/oteracil potassium, (2) at least one ingredient selected from the group consisting of folinic acid and pharmacologically acceptable salts thereof, and (3) cis-oxalate(1R,2R-diaminocyclohexane)platinum(II); a kit comprising a combination of pharmaceutical compositions for treating cancer in a mammal, comprising: (a) a combination drug of tegafur/gimeracil/oteracil potassium in a therapeutically effective amount; (b) a composition containing at least one ingredient selected from the group consisting of folinic acid and pharmacologically acceptable salts thereof in an amount effective for enhancing antitumor effects, and (c) a composition containing cis-oxalate(1R,2R-diaminocyclohexane)platinum(II) in an amount effective for enhancing antitumor effects; and a method for treating cancer.