Decidualization is a critical step during embryo implantation and characterized by the differentiation of endometrial stromal cells (ESCs) into decidual cells. Because miRNAs are important determinants of cellular fate specification, in this study, the miRNA expression in ESCs during in vitro decidualization was profiled by using a microarray. Significance analysis of microarrays revealed that 49 miRNA genes were differently (>2-fold) expressed between the noninduced ESCs and induced ESCs with a false discovery rate of 0. The expression variance of hsa-miR-222, 221, 143, 101, 30d, 30c, 181b, 27b, 29b, 507, and 23a was validated by using quantitative PCR (P < 0.05). Based on microRNA (miRNA) and mRNA expression variance and predicted target genes of miRNAs, a bioinformatic model of miRNAs controlling ESCs differentiation was formulated. Finally, we proved that down-regulation of has-miR-222 could decrease the number of cells in S phase during ESCs differentiation (P < 0.05). Antisense oligonucleotides of has-miR-222 could increase reporter gene expression by targeting the 3' untranslated regions of CDKN1C/p57kip2 mRNAs as well as increase CDKN1C/p57kip2 protein levels (P < 0.05). In conclusion, our results suggest that a subset of miRNAs play a key role in gene reprogramming during ESCs decidualization and that hsa-miR-222 participates in ESC differentiation by regulating ESCs terminally withdrawing from the cell cycle.