Hypotheses proposed to design nonthrombogenic polymer surfaces include, 1) phase-separated microdomain surfaces, 2) hydrophilic surfaces, 3) bioactive molecule incorporated surfaces and 4) biomembrane-like surfaces. In order to clarify the relationship between these surface design and their blood compatibility, we evaluated platelet adhesion and complement activation on these surfaces using an epifluorescent video microscopy (EVM) system, and analyzed adsorbed proteins on these surfaces using a sheep chronic left ventricular assist device (LVAD) model. The results are as follows; 1) thrombogenesis depends on the amount of adhered platelet at the initial contact with blood on the surfaces, 2) nonthrombogenicity of the blood contacting surfaces is dependent on the thickness, conformation and components of adsorbed proteins on the surfaces and 3) complement activation is not correlated with the amount of adhered platelet.