MicroRNAs have been demonstrated to regulate proliferation and apoptosis in many types of cancers, but biological functions in osteosarcomas remain relatively unknown. Here, we found expression of miR-802 to be up-regulated in osteosarcoma tissues in comparison with adjacent normal tissues. Enforced expression of miR-802 was able to promote cell proliferation in U2OS and MG63 cells, while miR-802 antisense oligonucleotides (antisense miR-802) inhibited cell proliferation. At the molecular level, our results further revealed that expression of p27, a negative cell-cycle regulator, was negatively regulated by miR-802. Therefore, the data reported here indicate that miR-802 is an important regulator in osteosarcoma, our findings contributing to a better understanding of important mis-regulated miRNAs in this tumour type.