Objective:MicroRNA-199a-3p (miR-199a-3p) is down-regulated in many kinds of tumors,including osteosarcoma. This study was aimed to investigate the effect of miR-199a-3p on apoptosis of human osteosarcoma cells (U2-OS). Methods:Human osteosarcoma cells(U2-OS) were transfected with miR-199a-3p mimics or negative control mimics (NC mimics) as negative control. MiR-199a-3p expression level was detected by quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR). Expression level of myeloid cell leukemia-1 (MCL-1) protein and cleavage of poly ADP-ribose polymerase(PARP) were detected by Western blot. Cell apoptosis was detected by flow cytometry. Results:Compared with control group,miR-199a-3p expression level of experiment group was significantly up-regulated,MCL-1 protein expression was reduced,cleavage level of PARP was increased and cell apoptosis rate of experiment group was significantly increased. The differences between experimental and control groups have statistical significance(P < 0.05). Conclusion:MiR-199a-3p can dramatically promote apoptosis of human osteosarcoma cells.