Osteosarcoma (OS), a malignant mesenchymal sarcoma, is the most frequent primary bone tumor, with a peak incidence in young children and adolescents. The downregulation of microRNA‑145 (miRNA/miR‑145) has previously been identified to be associated with the aggressiveness and metastasis of OS. However, the detailed regulatory mechanism by which miR‑145 inhibits OS remains largely unknown. The present study demonstrated that miR‑145 was significantly downregulated in OS tissues and KHOS and U2OS cell lines. Rho‑associated protein kinase 1 (ROCK1), a key regulator of actin cytoskeleton reorganization, was identified as a novel target of miR‑145. Ectopic expression of miR‑145 notably suppressed the protein expression of ROCK1 without affecting its mRNA level. Furthermore, the expression of ROCK1 was significantly increased in the OS tissues and in the KHOS and U2OS cells. It was further demonstrated that the overexpression of miR‑145 downregulated KHOS and U2OS cell proliferation and invasion, which was reversed by restoration of ROCK1. To the best of our knowledge, the present study demonstrates for the first time that, as a tumor suppressor, miRNA‑145 inhibits OS cell proliferation and invasion, at least in part by directly targeting ROCK1. These results indicate that miR‑145 may be a potential candidate for the diagnosis and treatment of OS.