Quantum dot (QD) is widely used as fluorescent labeling dye for its strong anti-fluorescence quenching, high quantum yield, wide absorption spectra, and narrow emission spectra. In the present paper, QD 585-labeled DNA methyltransferases (Dnmts) and Hoechst 33342-labeled chromosomes were imaged simultaneously using two-photon imaging system. The authors’ results showed that aging mouse oocytes may be not suitable for in-vitro maturation: both the localizations and expression levels of Dnmts in in-vitro matured oocytes of aging mice were changed, and these changes may be related to the abnormal DNA methylation modification.