Osteosarcoma (OS) is one of the most common malignancies of the bone. Although prognosis of OS has improved significantly during the past several years due to more intensive chemotherapy and radiotherapy regimens, new therapeutic approaches are needed for recurrent and inoperable cases, p73 and p63, like their homologue, the tumor suppressor p53, are able to induce apoptosis in several cell types. Here, we evaluated the antitumor effects of p73 and p63 on eleven different human OS cell lines. In vitro, adenovirus-mediated transduction of p63gamma induced apoptosis in OS cells that are resistant to p53-mediated apoptosis, while less effect was observed following transduction of p73alpha or p63alpha. Interestingly, the apoptotic effects of p63gamma were greater than those of wild-type p53 in OS cells carrying MDM2-amplification. We then determined the in vivo therapeutic effect of intratumoral injection of adenovirus-vector expressing p53 family members on xenografts derived from Saos-2 cells implanted in nude mice, and showed that infection with p63y significantly suppressed tumor growth compared with p53. In addition, exogenous p73beta and p63gamma significantly increased the chemosensitivity of OS cells to doxorubicin and cisplatin, chemotherapeutic agents commonly used in the treatment of OS. Our results suggest that adenovirus-mediated transduction of p53 family members may have utility in gene therapy for OS, particularly in combination with chemotherapeutic agents.