Objective: To explore the mechanism of large-scale transcriptional silence during germinal vesicle (GV) oocytes maturation in mice. Methods:The separated GV oocytes were obtained from 4~6-week-old ICR female mice. As for the observation about the expressional and distributional changes of both markers in the process of the chromatin configuration from non-surround nucleolus(NSN) type into surround nucleolus(SN) type in mice GV oocytes, these oocytes were immunofluorescence stained with RNA polymeraseⅡ antibody(anti-RNA PolⅡCTD, clone 4H8) and the second serine phosphorylated antibody at RNA polymeraseⅡCTD group (anti-RNA PolⅡCTD Ser2-P, clone H5); as well as histone H3K4/H3K9 tri-methylation antibodies (anti-H3K4me3, anti-H3K9me3). Results:In NSN type GV oocytes, RNA CTD PolⅡSer2-P was distributed with characteristic plaques shape in nucleus; meanwhile, H3K4me3 also presented the strong positive signals in nucleus. However, in SN type oocytes, RNA CTD PolⅡSer2-P lost the characteristic distribution and diffused in nucleus; moreover, the positive signal in nucleus showed by H3K4me3 disappeared. Conclusion:The reduction of RNA polymeraseⅡactivity and the change of histone modification status played an important role in the large-scale transcriptional silencing during germinal vesicle oocytes maturation of mice.