Accumulating evidence has shown that microRNAs are involved in multiple processes in cancer development and progression. Recently, miR-335 has been identified as a tumor-suppressing microRNA in many human cancers. However, the specific function of miR-335 in osteosarcoma is unclear at this point. In this study, we found that the expression of miR-335 in osteosarcoma tissues and cell lines was much lower than that in normal control, respectively, and the downregulated miR-335 was significantly associated with lymph-node metastasis. Transfection of miR-335 mimics could significantly inhibit the cell migration and invasion in MG-63 and U2OS osteosarcoma cell lines. Moreover, we also showed that ROCK1 was negatively regulated by miR-335 at the posttranscriptional level, via a specific target site within the 3'UTR by luciferase reporter assay. The expression of ROCK1 was inversely correlated with miR-335 expression in osteosarcoma tissues, and knockdown of ROCK1 by siRNA-inhibited osteosarcoma cells migration and invasion resembling that of miR-335 overexpression. Thus, our findings suggest that miR-335 acts as tumor suppressor by targeting the ROCK1 gene and inhibiting osteosarcoma cells migration and invasion. The findings of this study contribute to current understanding of the functions of miR-335 in osteosarcoma.