We examined plasma protein adsorption and platelet adhesion to polysulfone (PSf) flat membranes coated with Pluronic with varying polyethylene oxide (PEO) block length. Adsorption of albumin, globulin and fibrinogen to Pluronic-coated PSf membranes was independent of plasma dilution when concentrations of human blood plasma above 20% were applied. Increasing coating concentrations of aqueous Pluronic solution resulted in decreased protein adsorption by the PSf membranes. Pluronic F68, which was more hydrophilic than Pluronic L62 or L64 and had 80% of PEO content, was the most effective at suppressing the adsorption of plasma proteins and platelet adhesion to PSf membranes. We developed a mixed protein solution containing human albumin, gamma-globulin and fibrinogen to attempt to mimic the competitive and cooperative binding effects found in plasma. Fibrinogen adsorption from plasma could be recapitulated by the mixed protein solution. The number of platelets adhering to the PSf membranes decreased as the coating concentration of Pluronic solution was increased, and platelet adhesion decreased in parallel with fibrinogen adsorption. These results suggest that the bioinert property of PEO segments in the Pluronic, which is ascribed to their high flexibility in aqueous media, suppresses the adsorption of plasma proteins and platelets to the Pluronic-coated PSf membranes.