Osteosarcoma is the most common primary bone tumor in children and adults. Despite improved prognosis, resistance to chemotherapy remains responsible for failure of osteosarcoma treatment. The identification of the molecular signals that contribute to the aberrant osteosarcoma cell growth may provide clues to develop new therapeutic strategies for chemoresistant osteosarcoma. Here we show that the expression of ErbB3 is increased in human osteosarcoma cells in vitro. Tissue microarray analysis of tissue cores from osteosarcoma patients further showed that the ErbB3 protein expression is higher in bone tumors compared to normal bone tissue, and is further increased in patients with recurrent disease or soft tissue metastasis. In murine osteosarcoma cells, silencing ErbB3 using shRNA decreased cell replication, cell migration and invasion, indicating that ErbB3 contributes to tumor cell growth and invasiveness. Furthermore, ErbB3 silencing markedly reduced tumor growth in a murine allograft model in vivo. Immunohistochemal analysis showed that the reduced tumor growth induced by ErbB3 silencing in this model resulted from decreased cell osteosarcoma cell proliferation, supporting a role of ErbB3 in bone tumor growth in vivo. Taken together, the results reveal that ErbB3 expression in human osteosarcoma correlates with tumor grade. Furthermore, silencing ErbB3 in a murine osteosarcoma model results in decreased cell growth and invasiveness in vitro, and reduced tumor growth in vivo, which supports the potential therapeutic interest of targeting ErbB3 in osteosarcoma.