The main product obtained by oxidation of 2'-deoxycytidine with hydrogen peroxide is 2'-deoxycytidine N-oxide. Although its chemical synthesis and properties of 2'-deoxycytidine N-oxide have been well established, little has been reported about the chemical and biochemical behavior of DNA oligomers containing this modified deoxynucleoside. In this study, we synthesized DNA oligomers containing 2'-deoxycytidine N-oxide by use of a post-synthetic oxidative method. It should be noted that this modified base could be incorporated in oligodeoxynucleotides at appropriate positions by this strategy. The ability of the base pair formation was significantly low because of the blocking of the canonical hydrogen bonding site.