Novel 5'-deoxy-cytidine derivatives represented by the general formula (I) wherein R1 is a hydrogen atom or a group easily hydrolyzable under physiological conditions； R2 is a hydrogen atom, or -CO-OR4 group [wherein R4 is a saturated or unsaturated, straight or branched hydrocarbon group consisting of one to fifteen carbon atoms, or a group of the formula -(CH2)n-Y (in which Y is cyclohexyl or phenyl； n is an integer from 0 to 4)]； R3 is a hydrogen atom, bromo, iodo, cyano, a C1-4 alkyl group [which may be substituted with halogen atom(s)], a vinyl or ethynyl group [which may be substituted with halogen atom(s), C1-4 alkyl, cycloalkyl, aralkyl, or aromatic ring which may have one or more hetero atom(s)], or an aralkyl group which may be substituted for use in medical therapy, especially tumor therapy.
