Objective To investigate the expressions of H3K9 methyltransferases(KMTs) and demethylases(KDMs) in the liver of different aged mice. Methods Two-week, four-week and six-week old mice were killed and their liver tissues collected. Both mRNA and protein from the mice liver were extracted using Trizol kit and sonicated method respectively. Reverse transcription-quantitative real time polymerase chain reaction (RT-qPCR) was performed for mRNA expressions of several kinds of H3K9 methyltransferases and demethylases.The levels of H3K9 demethylases KDM3A and KDM4B proteins were determined using Western blotting. Results The mRNA expressions of several KMTs(including KMT1C, KMT1E and PRDM2 ) and KDMs(including KDM3A, KDM3B, KDM4A and KDM4B) were obviously different in the different developmental stages of a mouse’s liver( EM>P/EM> 0.05, EM>n/EM>=5).The levels of KDM3A and KDM4B proteins in the mice liver were also distinct, and both proteins in six-week old mice were lower than those in two-week and four-week old mice ( EM>P/EM> 0.05,EM>n/EM>=3). Conclusion The H3K9 methylation status of specific gene loci may be closely associat