To clarify the antiangiogenetic activity of chondromodulin-I (ChM-I), which is a cartilage-specific extracellular matrix (ECM) component, the effect of ChM-I on the four steps of angiogenesis were investigated in vitro. ChM-I markedly inhibited ECM invasion, the first step of angiogenesis, and migration of endothelial cells, the second step of angiogenesis. The proliferation of endothelial cells, the third step, was completely inhibited by ChM-I. Additionally, ChM-I suppressed the cell attachment of endothelial cells and caused the cells to undergo an apoptosis-like morphogenesis. In the final step, imperfect formation of tubelike cellular networks of endothelial cells was caused by ChM-I. ChM-I showed remarkable inhibitory effects on all four steps of angiogenesis in vitro, suggesting that ChM-I is a prominent regulator of the biological condition and that it would be a strong candidate as an antiangiogenic agent for biomedics.