An object of the present invention is to further enhance the antitumor effect when oxaliplatin is administered in combination with a combination drug containing tegafur, gimeracil and oteracil potassium. According to the present invention, by using oxaliplatin encapsulated in a liposome preparation, combination therapy of oxaliplatin plus a combination drug containing tegafur, gimeracil and oteracil potassium, is revealed to show remarkably enhanced antitumor effect without increasing side effects.本發明課題係進一步增強奧沙利鉑與替加氟、吉美拉西、奧替拉西鉀(Tegafur‧Gimeracil‧Oteracil Potassium)混合劑併用時的抗癌效果,依據本發明,藉由將奧沙利鉑作成脂質體製劑,在與替加氟‧吉美拉西‧奧替拉西鉀混合劑併用時,可在不增強副作用的情況下,顯著增強抗癌效果。