The present invention provides a novel antimetabolic anticancer agent that has an excellent balance between antitumor effect and toxicity. Specifically, the present invention provides a medicament containing, as an active ingredient, a 5-fluorouracil derivative represented by Formula (I) or a salt thereof: wherein R 1 represents a hydrogen atom or a protecting group of a hydroxy group, R 2 represents a lower alkoxy-lower alkyl group or a tetrahydrofuranyl group, X represents a carbon atom or a nitrogen atom, and Y represents a halogen atom or a cyano group.本發明係以提供一種抗腫瘤效果與毒性的平衡優良之新穎的代謝拮抗抗癌劑作為目的。本發明係提供5-氟尿嘧啶衍生物或其鹽、及含有新穎的該5-氟尿嘧啶衍生物或其鹽作為有效成分之醫藥,該5-氟尿嘧啶衍生物或其鹽係由通式(I)所表示,[式中,R1係表示氫原子或羥基的保護基。R2係表示低級烷氧基低級烷基或四氫呋喃基。X係表示碳原子或氮原子。Y係表示鹵素原子或氰基]。
