Polyurethane (PU) is widely used to make artificial heart and blood vessel wells; however, its thrombogenicity in vivo is still in question. The biomembrane-mimetic and water-soluble polymers, poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB), were used to modify polyurethane (PU) surfaces for improving their hemocompatibility. The morphologies of the PMB modified PU surfaces were examined by using atomic force microscopy and the parameters of the PMB absorption kinetics were extracted from dynamic water contact angle measurements. Two-phase domains, the hard and soft segment phases, were observed on the PU surfaces under the aqueous conditions. The absorbed PMB molecules formed the isolated layers first on the hydrophobic hard segments, and subsequently networked as the PMB concentration increased. The increments of PMB concentration led to the decrement of the effective molar activation (wetting) free energy DeltaG.