15-Lipoxygenase-1 (15-LO-1) is involved in many pathological processes. The purpose of this study was to determine the potential role of 15-LO-1 in osteoarthritis (OA). The levels of 15-LO-1 expression were measured by western blotting and quantitative real-time PCR in articular cartilage from the OA rat models and OA patients. To further investigate the effects of 15-LO-1 on chondrocyte functions, such as extracellular matrix (ECM) secretion, the release of matrix-degrading enzymes, the production of reactive oxygen species (ROS), cell proliferation and apoptosis, we decreased or increased 15-LO-1 expression in chondrocytes by means of transfecting with siRNA targeting 15-LO-1 and plasmid encoding 15-LO-1, respectively. The results showed that 15-LO-1 expression was obviously increased in articular cartilage from OA rats and OA patients. It was also found that many factor-related OA, such as mechanical loading, ROS, SNP and inflammatory factor, significantly promoted 15-LO-1 expression and activity in chondrocytes. Silencing 15-LO-1 was able to markedly alleviate mechanical loading-induced cartilage ECM secretion, cartilage-degrading enzyme secretion and ROS production. Overexpression of 15-LO-1 could inhibit chondrocyte proliferation and induce chondrocyte apoptosis. In addition, reduction of 15-LO-1 in vivo significantly alleviated OA. Taken together, these results indicate that 15-LO-1 has an important role in the disease progression of OA. Thus 15-LO-1 may be a good target for developing drugs in the treatment of OA.