NBAT1 functions as a tumor suppressor in some cancers. However, the expression pattern,the biological function and the mechanisms of NBAT1 in OS progress have not been elucidated. In this study, for the frst time, we found that NBAT1 expression is downregulated in OS tissues and cell lines and is associated with clinical stage, distant metastasis and poor prognosis. Loss- and gain-of-function assays showed that NBAT1 played a negative regulatory role in OS growth and metastasis in vitro and in vivo. Further investigation demonstrated that NBAT1 physically interacted with miR-21 and then suppressed its expression. NBAT1 also regulated downstream genes targeted by miR-21, including PTEN, PDCD4, TPM1 and RECK.