Differentiation and epithelial-mesenchymal transition (EMT) in mammary epithelial cell were analyzed with respect to the epigenetic gene regulation. In the first part, the chromatin accessibility at the beta-casein promoter and the role of histone 3 lysine 9 Dimethylation (H3K9me2) in transcriptional regulation of beta-casein gene in HC11 cells were studied. Moreover, the function of the JmjC domain-containing demethylase Jmjd1a in beta-casein expression was also analyzed. The results revealed that the beta-casein promoter is inaccessible in HC11 cells, and the inaccessibility is independent of hormone treatment. Moreover, the repressive histone mark H3K9me2 is associated at beta-casein promoter. Since the associated H3K9me2 is correlated to chromatin inaccessibility, it probably represses the beta-casein gene. Although the overexpression of Jmjd1a essential domains reduces global H3K9me2 level, beta-casein expression is still not upregulated. This is, at least in part, due to the inhibitory effect of Jmjd1a domains on transcription machinery. In the second part, the role of histone 3 lysine 27 Trimethylation (H3K27me3) in regulation of EMT was analyzed. The finding revealed that H3K27me3 regulates EMT at levels of marker genes, Snail, but not the master regulator. The promoters of both epithelial marker Cdh1 and the mesenchymal marker Acta2 are associated with H3K27me3 and the associations correlate to gene transcription. In addition, Snail is a target of H3K27me3, since removal of H3K27me3 by both DZNep and Suz12 knockdown can equally enhance the TGFβ3 mediated induction of Snail mRNA. TGFβ3 is essential. Finally, the CBF-A/KAP-1/FTS-1 complex might not be regulated by H3K27me3. Besides, DZNep is identified to be a novel EMT inducer and the effect results, at least in part, from the activation of the CBF-A/KAP-1/FTS-1 complex.