Numerous studies have recently suggested that miRNAs contribute to the development of various types of human cancer as well as to their proliferation and metastasis. The aim of this study was to investigate the functional significance of miR-126 and to identify its possible target genes in osteosarcoma (OS) cells. Here, we found that expression level of miR-126 was reduced in osteosarcoma cells in comparison with the adjacent normal tissues. The enforced expression of miR-126 was able to inhibit cell proliferation in U2OS and MG63 cells, while miR-126 antisense oligonucleotides (antisense miR-126) promoted cell proliferation. At the molecular level, our results further revealed that expression of Sirt1, a member of histone deacetylase, was negatively regulated by miR-126. Therefore, the data reported here demonstrate that miR-126 is an important regulator in osteosarcoma, which will contribute to better understanding of the important misregulated miRNAs in osteosarcoma cells.