An increasing body of evidence indicates that microRNAs (miRNAs), a class of small non‑coding RNAs, are often aberrantly expressed in human osteosarcoma. This study aimed to investigate the effects of miR‑25 and to identify its potential target genes in osteosarcoma (OS) cells. First, the expression of miR‑25 was detected by reverse transcription‑quantitative polymerase chain reaction (RT-qPCR), which revealed a significant upregulation of miR‑25 in osteosarcoma tissues compared to the adjacent healthy tissues. To investigate the role of miR‑25 in osteosarcoma cell proliferation, the miR‑25 precursor was next transfected into Saos‑2 and U2OS cells. Overexpression of miR‑25 promoted cell proliferation in vitro and tumor growth in a xenograft mouse model. In addition, our results revealed that the protein expression of p27, a cell‑cycle inhibitor, is negatively regulated by miR‑25. Restoring the p27 level in miR‑25‑overexpressing cells reversed the enhancing effect of miR‑25 on cell proliferation. Therefore, miR‑25 may act as an onco‑miRNA in osteosarcoma, which provides new perspectives in cancer treatment strategies based on molecular targeting.