ObjectiveTo investigate the function and possible mechanism of microRNA-199b-5p (miR-199b-5p) in Ewing's sarcoma cell lines so as to provide theoretical basis for biological treatment in the future. MethodsA673 cells and TC252 cells were adopted as Ewing's sarcoma cell lines in vitro. miR-199b-5p oligonucleotide fragments (mimic) and scramble control (mimic control) were used to transfect TC252 cells and A673 cells, respectively. The expression of miR-199b-5p was measured in 2 cell lines by real-time quantitative-PCR and compared with that in mesenchymal stem cells (MSCs). The cell proliferation was examined by cell counting kit 8. The cell cycle and apoptosis were detected by flow cytometry. The possible targets of miR-199b-5p were determined by luciferase assays. The protein expressions of possible targets were measured by Western blot. ResultsThe expression of miR-199b-5p in control group was significantly down-regulated in A673 cells and TC252 cells when compared with that in MSCs (P<0.05); and the expression of miR-199b-5p in experimental group was significantly up-regulated when compared with that in control group (P<0.05). G1 phase cells increased obviously and S phase cells decreased significantly compared with corresponding cells in control group (P<0.05); but no significant difference was found in G2/M phase cells between 2 groups (P>0.05). The apoptosis rate increased significantly in experimental group when compared with that in control group (P<0.05). The possible targets of miR-199b-5p were cyclin-L1 (CCNL1) and c-Kit by luciferase assays. Western blot results showed that the CCNL1 and c-Kit protein expression levels in experimental group were significantly lower than those in control group (P<0.05). ConclusionmiR-199b-5p can suppress the cell proliferation, block the cell cycle, and promote the cell apoptosis, so miR-199b-5p inhibits Ewing's sarcoma cell lines by targeting CCNL1 and c-Kit.