MicroRNA-199a-3p is downregulated in human osteosarcoma and regulates cell proliferation and migration. microRNAs (miRNA, miR) play an important role in cancer cell growth and migration; however, the potential roles of miRNAs in osteosarcoma remain largely uncharacterized. By applying a miRNA microarray platform and unsupervised hierarchical clustering analysis, we found that several miRNAs have altered expression levels in osteosarcoma cell lines and tumor tissues when compared with normal human osteoblasts. Three miRNAs, miR-199a-3p, miR-127-3p, and miR-376c, were significantly decreased in osteosarcoma cell lines, whereas miR-151-3p and miR-191 were increased in osteosarcoma cell lines in comparison with osteoblasts. Transfection of precursor miR-199a-3p into osteosarcoma cell lines significantly decreased cell growth and migration, thus indicating that the inhibition effect is associated with an increase in the G(1)-phase and a decrease of the S-phase cell population. In addition, we observed decreased mTOR and Stat3 expression in miR-199a-3p transfected cells. This study provides new insights for miRNAs in osteosarcoma and suggests that miR-199a-3p may play a functional role in osteosarcoma cell growth and proliferation. Restoring miR-199a-3p's function may provide therapeutic benefits in osteosarcoma.©2011 AACR