Purpose: Many studies have revealed that microRNAs (miRNAs) play crucial roles in cancer development and progression. miRNA-217 (miR-217) has been implicated in various cancers. However, the role of miR-217 in osteosarcoma (OS) remains unclear. In this study, the authors examined the role of miR-217 in development of OS. Materials and Methods: Using quantitative real-time PCR, they assessed expression levels of miR-217 in cultured cells and patient samples and examined the proliferation, migration, and invasion of cultured cells by MTT cell proliferation assays, cell scratch test, and cell transwell test. The proliferation, migration, and invasion were examined for MG63 and U2OS transfected by miR-217. Silent information regulator 2 homolog 1 (SIRT1) overexpression plasmid was designed. Results: Expression of miR-217 was downregulated in samples of OS tissue and cultured cells. Proliferation, migration, and invasion were inhibited by ectopic overexpression of miR-217. SIRT1 was identified as targets of miR-217. Expression levels of SIRT1 were inhibited by miR-217 expression in cultured cells, and the expression levels of miR-217 and SIRT1 were inversely correlated in patients with OS. Conclusion: MiR-217 acts as a tumor suppressor in the development of OS. The tumor-suppressive function of miR-217 in OS suggests inhibition of SIRT1.