Osteosarcoma and chondrosarcoma are rare and aggressive tumors representing less than 1% of all malignancies of the maxillofacial region. In many cases these tumors exhibit similar histopathologic features. Objectives: The aim of this study was to verify in these tumors the immunohistochemical expression of the bone extracellular matrix (ECM) proteins: osteonectin (ONC), osteopontin (OPN), bone sialoprotein (BSP) and osteocalcin (OCC). Methods: Three cases of osteosarcomas and three cases of chondrosarcomas were retrieved from the archives of the Surgical Pathology Service, School of Dentistry, University of São Paulo and submitted to the streptavidin-biotin immunohistochemical methods. Results: The results showed a heterogeneous expression of the proteins analyzed in the different areas of each case. In the mineralized areas of both tumors staining was variable with no significant difference between the tumors. The osteoblasts exhibited a weak expression of ONC and OPN and a moderate expression of BSP. The chondroblasts showed a weak expression of ONC and BSP and a moderate expression of OPN. The mesenchymal cells of both tumors demonstrated a slight positivity of ONC and a moderate positivity of BSP. However, in chondrosarcomas these cells presented a weak expression of OPN that was absent in osteosarcomas. Conclusions: These results suggest that the expression of the bone ECM in the tumors studied varies according to cellular differentiation, thus, the study of these proteins may determine immunohistochemical markers that can help in the differentiation of these tumors.