The selective detection of 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA without chemical or enzymatic treatment is an attractive tool for genomic research. We designed and synthesized the non-natural nucleoside analogue, the adenosine-1,3-diazaphenoxazine (Adap) derivative, for selective recognition of 8-oxo-dG in DNA. This study clearly showed that Adap has a highly selective stabilizing effect on the duplex containing the Adap 8-oxo-dG base pair. Furthermore, the fluorescent property of Adap was shown to be useful for the selective detection of 8-oxo-dG in the duplex DNA. To the best of our knowledge, this is the first successful demonstration of a non-natural nucleoside with a high selectivity for 8-oxo-dG in DNA.