Deoxycytidine (IUPAC name: 2′-Deoxycytidine) is a deoxyribonucleoside, a component of deoxyribonucleic acid. 2′-Deoxycytidine is similar to the ribonucleoside cytidine but with one hydroxyl group removed from the C2' position. It has a role as a human metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite. It is functionally related to a cytosine.

Deoxycytidine can be phosphorylated at C5' of the deoxyribose by deoxycytidine kinase, converting it to deoxycytidine monophosphate (dCMP), a DNA precursor. dCMP can be converted to dUMP and dTMP.

It can also be used as a precursor for 5-aza-2′-deoxycytidine, a treatment for MDS patients. This compound slows the cell cycle by interfering with the methylation of the P15/INK4B gene, increasing the expression of the P15/INK4B protein, which subdues the transformation of MDS to leukemia.

The kinase that converts deoxycytidine to its 5’-monophosphate has been studied extensively in preparations from the calf thymus (35, 36). The preferred substrate is deoxycytidine, for which the Michaelis constant (5 × 10–6 M) is much lower than that of two other substrates, deoxyadenosine and deoxyguanosine. Cytidine, uridine, and thymidine are not phosphorylated by this enzyme. Deoxycytidine kinase is subject to a complex pattern of allosteric regulation by nucleotides. The end product of deoxycytidine phosphorylation, dCTP, is a potent inhibitor; this inhibition is reversed by dTTP. The enzyme has a rather broad specificity for the phosphate donor, with the triphosphates of the natural ribo- and deoxyribonucleosides being substrates; the inactivity of dCTP is a notable exception.