In vitro evaluation of antithrombogenicity of materials of artificial vascular vessels was carried out based on an analysis of the coagulation mechanism of blood. Coagulation of blood in tubes coated with endothelial cells (ECs) or segmented polyurethane (SPU) was measured by a rheological technique. Coagulation of blood in hybrid-type vascular vessel model tubes consisting of cultured ECs proliferated on carbon-deposited SPU was also examined. Coagulation of blood in these tubes occurred within 40 min, and appears to be due to the interaction between erythrocytes and a coagulant factor in the plasma. From the in vitro evaluation test, when the time of onset of the coagulation of blood in contact with a surface of the artificial materials is longer than 20–30 min, the materials can be considered to provide an inert surface against thrombus formation and blood coagulation.