Cellular DNA is constantly exposed to the risk of oxidation. 8-oxoguanine (8-oxoG) is one of the major DNA lesions generated by oxidation, which is primarily corrected by base excision repair. When it is not repaired prior to replication, replicative DNA polymerases yield misinsertion of an adenine (A) opposite the 8-oxoG on the template strand, generating an A:8-oxoG mispair. MYH, a mammalian homolog of Escherichia coli MutY, is a DNA glycosylase responsible for initiating base excision repair of such a mispair by excising the adenine opposite 8-oxoG. Here, using an in vivo repair system, we show that DNA replication enhances the repair of the A:8-oxoG mispair. Repair efficiency was lower in MYH-deficient murine cells than in MYH-proficient cells. Transfection of the MYH-deficient cells with a wild-type MYH expression vector increased the efficiency of A:8-oxoG repair, indicating that a significant part of this replication-associated repair depends on MYH. Expression of a mutant MYH in which the PCNA binding motif was disrupted did not increase the repair efficiency, thus suggesting that the interaction between PCNA and MYH is critical for MYH-initiated repair of A:8-oxoG.