The present invention provides a kind of antitumor effect fortifier, it is using uracil compound shown in formula (I) or its pharmaceutically acceptable salt as effective component, (in general formula (I), X indicates C1-5 alkylidenes, constituting one of methylene of the alkylidene can be replaced by oxygen atom, R1 indicates that hydrogen atom or C1-6 alkyl, R2 indicate that hydrogen atom or halogen atom, R3 indicate C1-6 alkyl, C2-6 alkenyls, C3-6 naphthenic base, (C3-6 naphthenic base) C1-6 alkyl, halogenation C1-6 alkyl or saturated heterocyclyl).本發明提供一種抗腫瘤效果增强劑，其是以式（Ⅰ）所示的尿嘧啶化合物或其藥學上可接受的鹽作爲有效成分，（通式（Ⅰ）中，X表示C1-5亞烷基，構成該亞烷基的亞甲基之一可以被氧原子取代，R1表示氫原子或C1-6烷基，R2表示氫原子或鹵原子、R3表示C1-6烷基、C2-6烯基、C3-6環烷基、（C3-6環烷基）C1-6烷基、鹵化C1-6烷基或飽和雜環基）。
