To elucidate the effect of guanine lesion produced by the oxidative damage on DNA, 1 nanosecond molecular dynamics simulations of native and oxidized DNA were performed. The target DNA molecules are dodecamer duplex d(CGCGAATTCGCG)₂ and its derivative duplex d(C₁G₂C₃(8-oxoG)₄A₅A₆T₇T₈C₉G₁₀C₁₁G₁₂)·d(C₁₃G₁₄C₁₅G₁₆A₁₇ A₁₈T₁₉T₂₀C₂₁G₂₂C₂₃G₂₄), which has one oxidized guanine, 7, 8-dihydro-8-oxoguanine (8-oxoG), at the fourth position. The local structural change due to the lesion of 8-oxoG and the global dynamic structure of the 8-oxoG DNA were studied. It was found that the 8-oxoG DNA remained structurally stable during the simulation due to newly produced hydrogen bonds around the (8-oxoG)₄ residue. However, there were distinguishable differences in structural parameters and dynamic property in the 8-oxoG DNA. The conformation around the (8-oxoG)₄ residue departed from the usual conformation of native DNA and took an unique conformation of ε-ζ in B_II conformation and ξ in high anti orientation at the (8-oxoG)₄ residue, and adopted a very low helical twist angle at the C₃:G₂₂ - (8-oxoG)₄:C₂₁ step. Further analysis by principal component analysis indicated that the formation of the hydrogen bonds around the (8-oxoG)₄ residue plays a role as a trigger for the conformational transition of the 8-oxoG DNA in the conformational space.