Abstract: To study the effect of aging on the expression of Dnmts in developmental stages of mouse preimplantation embryos, Western-blot was used to detect the expression of Dnmts in 2-cell, 4-cell, 8-cell embryos, morula and blastocysts of young and old mice, respectively. The results showed that no significant difference was found in Dnmt3 a expression between 2-cell and 4-cell embryos（P＞0.05）, however, the expression levels of Dnmt1, Dnmt3 b and Dnmt3 were found with a significant decrease in old mice（P＜0.05）. No significant difference was found in the expression levels of four DNA methyltransferases in 8-cell embryos, morula and blastocyst（P＞0.05）. It could be deduced that the fluctuation of Dnmts expression could be affected by aging in 2-cell, 4-cell embryos of mice.