Adsorption of proteins (fibrinogen, albumin, and gamma globulin) from plasma onto surface-modified PUs (PU-PEO, PU-SO3, and PU-PEO-SO3) was evaluated. Adsorbed fibrinogen at steady state decreased in the order PU-SO3 > PU > PU-PEO-SO3 > PU-PEO, suggesting that sulfonate groups have specific high affinity to fibrinogen. The intermediate fibrinogen adsorption on PU-PEO-SO3 can be explained by the compensatory effect between the low protein binding affinity of the PEO chain and the high fibrinogen binding affinity of the sulfonate group. In addition, PU-PEO-SO3 showed a very fast fibrinogen adsorption due to the high accessibility of the sulfonate group to fibrinogen by the poly(ethylene oxide) (PEO) spacer. The kinetic profiles of their surfaces showed that as the adsorption time increases, fibrinogen initially adsorbed was decreased and a plateau reached, demonstrating that all the surfaces exhibited the Vroman effect (the fibrinogen displacement phenomenon). PU-PEO showed the least fibrinogen and albumin adsorption among PUs, confirming the known nonadhesive property of PEO chains. It is very interesting that PU-PEO-SO3 exhibited the highest adsorption of albumin and the lowest adsorption of IgG. Therefore, it may be concluded that such adsorption behaviors of proteins to PU-PEO-SO3 contribute to improved blood compatibility.