Objective：To investigate the expression profile of inhibitors of differentiation 3（Id3） in the endometrium of early pregnant mice and artificially induced pregnant mice，and the role of Id3 gene in decidualization. Methods：Western blot and qRT-PCR were used to detect the expression of Id3 in uterus of early pregnancy and artificial induced decidualization model. The effect of Id3 expres－sion on the decidualization of endometrial stromal cells was analyzed by the decidualization and overexpression of Id3 gene induced by the isolated endometrial stromal cells of primary mice in vitro. Results：The Id3 highly expressed in the early pregnancy model of mice in the endometrial receptivity stage（the fourth day of pregnancy）（Pprotein=0.001；PmRNA=0.001），and lower expressed in decid－ualized uterus after embryonic implantation（PD5protein=0.026；PD5mRNA=0.038）. The expression of Id3 in artificial induced endometrium was significantly lower than that in the control group（Pprotein=0.005；PmRNA=0.000）. In vitro induced decidualization inhibited the expres－sion of Id3 gene（Pprotein=0.000；PmRNA=0.001）. Overexpression of Id3 significantly reduced the process of decidualization of endometrial stromal cells in vitro；Stat3 signaling was involved in the process of decidual stromal cells regulated by Id3. Conclusion：Id3 is in－volved in the mice embryo implantation and regulates the decidualization of endometrial stromal cells.