A 5-fluorouracil derivative represented by Formula below or a salt thereof: wherein R 1 represents a hydrogen atom or a protecting group of a hydroxy group, R 2 represents a C 1-6 linear or branched alkoxy-C 1-6 linear or branched 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; wherein the protecting group of a hydroxy group is selected from the group consisting of acyl groups; C 2-7 linear or branched alkoxycarbonyl groups; carbamoyl groups mono- or disubstituted by a C 1-6 alkyl group; substituted or unsubstituted C 1-6 linear or branched alkyl groups; C 2-6 linear or branched alkenyl groups; substituted or unsubstituted benzyl group, benzhydryl group or trityl group; silyl protecting groups; and amino acid residues; wherein the acyl groups are selected from the group consisting of substituted or unsubstituted C 2-6 aliphatic acyl groups, substituted or unsubstituted benzoyl group, α-naphthoyl group, or β-naphthoyl group and C 3-6 cycloalkyl carbonyl groups, wherein the substituents of substituted C 2-6 aliphatic acyl groups or the substituted benzoyl group, α-naphthoyl group, or β-naphthoyl group are 1 to 3 substituents selected from a C 1-6 linear or branched alkyl group, a C 1-6 linear or branched alkoxy group, a halogen atom, a nitro group, and a carboxy group; wherein the substituents of the substituted C 1-6 linear or branched alkyl group are 1 to 3 substituents selected from the group consisting of a halogen atom and a C 1-6 linear or branched alkoxy group; wherein the substituents of the substituted benzyl group, benzhydryl group or trityl group are 1 to 5 substituents selected from the group consisting of a C 1-6 linear or branched alkyl group, a C 1-6 linear or branched alkoxy group, a halogen atom, a nitro group and a cyano group; and wherein the silyl protecting groups are selected from the group consisting of a trimethylsilyl group, a tert-butyldimethylsilyl group, a methyldiisopropylsilyl group, a triisopropylsilyl group, a tetraisopropyldisiloxyl (TIPDS) group and a diphenylmethylsilyl group. wherein R 1 represents a hydrogen atom or a protecting group of a hydroxy group, R 2 represents a C 1-6 linear or branched alkoxy-C 1-6 linear or branched 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; wherein the protecting group of a hydroxy group is selected from the group consisting of acyl groups; C 2-7 linear or branched alkoxycarbonyl groups; carbamoyl groups mono- or disubstituted by a C 1-6 alkyl group; substituted or unsubstituted C 1-6 linear or branched alkyl groups; C 2-6 linear or branched alkenyl groups; substituted or unsubstituted benzyl group, benzhydryl group or trityl group; silyl protecting groups; and amino acid residues; wherein the acyl groups are selected from the group consisting of substituted or unsubstituted C 2-6 aliphatic acyl groups, substituted or unsubstituted benzoyl group, α-naphthoyl group, or β-naphthoyl group and C 3-6 cycloalkyl carbonyl groups, wherein the substituents of substituted C 2-6 aliphatic acyl groups or the substituted benzoyl group, α-naphthoyl group, or β-naphthoyl group are 1 to 3 substituents selected from a C 1-6 linear or branched alkyl group, a C 1-6 linear or branched alkoxy group, a halogen atom, a nitro group, and a carboxy group; wherein the substituents of the substituted C 1-6 linear or branched alkyl group are 1 to 3 substituents selected from the group consisting of a halogen atom and a C 1-6 linear or branched alkoxy group; wherein the substituents of the substituted benzyl group, benzhydryl group or trityl group are 1 to 5 substituents selected from the group consisting of a C 1-6 linear or branched alkyl group, a C 1-6 linear or branched alkoxy group, a halogen atom, a nitro group and a cyano group; and wherein the silyl protecting groups are selected from the group consisting of a trimethylsilyl group, a tert-butyldimethylsilyl group, a methyldiisopropylsilyl group, a triisopropylsilyl group, a tetraisopropyldisiloxyl (TIPDS) group and a diphenylmethylsilyl group.