MicroRNAs were recently found to participate in oncogenesis and growth of various tumors. We hypothesized that microRNA-223 (miR-223) plays a role in endometrial carcinoma growth. In this study, we transfected RL952 cells with lentivirus containing miR-223 precursor to establish a miR-223 over-expression model. Proliferation of the cells was greatly inhibited when miR-223 was over-expressed, and cell cycle progress was blocked in G0/G1 phase. To investigate the mechanisms involved, we scanned the putative target genes of miR-223 using bioinformatics, and confirmed that insulin-like growth factor-1 receptor (IGF-1R) was a functional target of miR-223 using quantitative PCR, Western blot and luciferase reporter assay. Meanwhile, over-expressed miR-223 was found to regulate the expression of IGF-1R by repressing protein translation. Silencing IGF-1R with small interfering RNA resulted in similar effect as miR-223 overexpression. Therefore, our data suggest that miR-223 regulates RL95-2 cells proliferation and cell cycle progress by targeting IGF-1R.