Endostatin derived from collagen XVIII is a potent endogenous anti-angiogenic factor that induces regression of various tumors of epithelial origin. Endostatin has been shown to inhibit endothelial cell functions, however, its effect remains controversial. We first attempted here to apply the inhibitory effect of recombinant human endostatin on chondrosarcomas, which originate from the mesenchyme, in nude mice. Endostatin induced reduction of chondrosarcoma growth and tumor angiogenesis in vivo. However, endostatin showed no effect on the proliferation and migration of chondrosarcoma cells in vitro. Next, we investigated the interactions between endostatin and endothelial cells in detail. Endostatin inhibited the migration on and attachment to collagen I but did not affect the proliferation of endothelial cells. Although the migration of endothelial cells was stimulated by angiogenic factors such as basic fibroblast growth factor and vascular endothelial growth factor, endostatin showed similar inhibitory effects on it in the presence and absence of the stimulants. Moreover, the inhibitory effect against endothelial cell attachment to collagen I was attenuated or modulated in the presence of neutralizing antibodies of α₂, α₅β₁, and α_vβ₃ integrins but not that of α₁ integrin. Our results suggest that endostatin might suppress the α₂β₁ integrin function of endothelial cells via α₅β₁ or α_vβ₃ integrin. We propose here that endostatin might be effective for anti-angio-genic therapy for human chondrosarcomas through the suppression of α₂α₁ integrin functions in endothelial cells.