【Objective】 To explore the effects of 22 demethylases of histone H3k4, H3k9, H3k27 and H3k36 on the differentiation of fetal mice brown adipocytes, so as to provide a theoretical basis for the study of differentiation of brown adipocytes. 【Methods】 We collected the embryos from pregnant mice at stages E13.5 to E19.5, with no less than 3 fetal mice obtained at each time point. Then we isolated interscapular brown adipose tissues(BAT) for HE staining and observed the differentiation of brown adipocytes under a microscope. Realtime RT-qPCR was used to test the expression of BAT markers such as Ucp1, Cidea and Prdm16, adipocyte differentiation related gene Pparγ and 22 lysine demethylases of histone H3 in BAT. Ucp1 protein expression in BAT was detected by Western blot. 【Results】 BAT were first observed in the interscapular area of fetal mice at E14.5. Lipid droplets were observed under light microscope in the brown adipocytes of fetal mice at E18.5. Compared with those in E15.5 embryos, in E16.5 to E19.5 embryos, the expression of Ucp1, Cidea, Prdm16 and Pparγ increased(P<0.05) and Ucp1 protein expression increased(P<0.05). Of H3k4 demethylases, Jarid1a, Jarid1b, Jarid1d and Lsd1 showed decrease in expression(P< 0.05); Jarid1c expression had no statistical significance(P>0.05). Of H3k9 demethylases, Jmjd2a, Jmjd2b, Jmjd2c, Phf2, Jmjd1c and Jhdm2a showed decrease in expression(P< 0.05); Phf8, Jhdm2b and Jmjd2d showed increase in expression(P<0.05); MINA expression had no statistical difference(P>0.05). Of H3k36 demethylases, Jmjd4, Jmjd5 and Jhdm1b showed decrease in expression(P<0.05); Jhdm1a showed increase in expression(P<0.05). Of H3k27 demethylases, Jmjd3, Utx and Jhdm1d showed increase in expression(P<0.05) . 【Conclusion】 In the process of brown adipocytes differentiation, expressions of H3k4 and H3k36 demethylases were mainly downregulated and those of some H3k9 and H3k27 demethylases were upregulated. These demethylases formed a complex regulatory network with transcriptional activation and transcriptional elongation as the main effects.