A novel pyrimidine nucleoside compound represented by the following formula (1) :(wherein one of X and Y represents a cyano group, and the other represents a hydrogen atom one of R1 and R2 represents a hydrogen atom, a carbonyl group having a C1-C6 alkyl group which has been mono-substituted by an amino group, or a group represented by (R3) (R4) (R5) Si-, and the other represents a silyl group represented by (R6) (R7) (R8) Si-, or R1 and R2 together form a 6-membered cyclic group represented by -Si(R9)(R10)- R3, R4, R5, R6, R7, and R8 each represent an alkyl group, a cyclic alkyl group, an aryl group, or an alkyl group which has been substituted by one or two aryl groups and R9 and R10 each represent an alkyl group) or a salt thereof. The novel pyrimidine nucleoside compound exhibits excellent anti-tumor effect as compared with existing pyrimidine nucleoside compounds.
