Osteosarcoma (Os) is the most common malignant bone tumor in childhood and not rare in adults. In recent years, much research has focused on the role of angiogenesis in tumor development, growth, invasion, and metastasis. The aims of this study were to characterize neovascularization established between the xenotransplanted Os and the host at histological, immunohistochemical, ultrastructural, and molecular level, and to evaluate if this model could be used in testing new anti-angiogenic drugs. Three xenotransplanted human Os were evaluated. Tumor pieces 3-4 mm in size were implanted subcutaneously on the back of athymic Balb-c nude mice (n = 14). The animals were killed at 24, 48, and 72 h and 7, 14, 21, and 28 days after implantation. Tumor samples were either fixed in 10 % formaldehyde and embedded in paraffin for histological analysis, or fixed with glutaraldehyde (2 %) for electron microscopy or retained non-fixed for molecular analysis (ELISA and qRT-PCR). Morphologically, intense neo-vasculogenesis within tumor parenchyma was present between the first and third week after transplantation. Immunohistochemistry demonstrated overexpression of VEGF and their receptors together with PDFGFRA 24-48 h after tumor implantation. Additionally, neoplastic cells co-expressed chemokines (CXCL9, CXCL10, and GRO) and their receptors. Molecular studies showed two expression profiles, distinguishing an early and a late phase in the angiogenic process. In Os, our model showed two stages of induced angiogenesis, with close association between histological and molecular events. This approximation could be of use for testing the effect of different anti-angiogenic agents.