Abnormal expression of long noncoding RNAs (lncRNAs) often contributes to the unrestricted growth and invasion of cancer cells. lncRNA X-inactive specific transcript (XIST) expression is upregulated in several cancers; however, its underlying mechanism in osteosarcoma (OS) has not been elucidated. In the present study, we found that XIST expression was significantly increased in OS tissues and cell lines by LncRNA Profiler and qRT-PCR. The effects of XIST and miR-320b on OS cell proliferation and invasion were studied by MTT and Transwell invasion assays. The competing relationship between XIST and miR-320b was confirmed by luciferase reporter assay. Our results showed that XIST knockdown strikingly inhibited cell proliferation and invasion. Furthermore, XIST could directly bind to miR-320b and repress miR-320b expression. Moreover, XIST overexpression significantly relieved the inhibition on OS cell proliferation and invasion mediated by miR-320b overexpression, which involved the derepression of Ras-related protein RAP2B. We propose that XIST is responsible for OS cell proliferation and invasion and that XIST exerts its function through the miR-320b/RAP2B axis. Our findings suggest that lncRNA XIST may be a candidate prognostic biomarker and a target for new therapies in OS patients.