Osteosarcoma is an aggressive cancer in skeletal system with unknown molecular mechanisms of etiology and pathogenesis, therefore it remains a challenge for current therapeutic strategies to effectively treat osteosarcoma. The aim of this review is to give an overview of the molecular and mechanistic changes identified in recent years which might be new targets for the treatment of osteosarcoma. These molecules play important roles in different biological and pathological programs of osteosarcoma, including the altered oncogenes and tumor suppressor genes, molecules involved in tumor cell migration and invasion, angiogenesis, apoptosis and proliferation, miRNAs, and molecules involved in osteoclast function and multidrug resistance. Further research on these molecules in osteosarcoma will provide new insights into the target therapy for osteosarcoma.