Polyurethanes are a class of polymers that have a wide range of applications in the medical field although their blood compatibility still needs improvement. In order to obtain medical purity, this study prepared membrane-form polyurethanes from toluene 2,4-diisocyanate (TDI) and poly(propylene ethylene glycol) without the addition of any ingredients such as solvents, catalysts, or chain extenders. The aim was to increase surface hydrophilicity and improve blood compatibility. Therefore, the prepared membranes were modified by treatment with oxygen or argon plasmas. Characterizations of the samples were achieved by contact-angle and water-uptake studies as well as from atomic force microscope (AFM) pictures. It was found that oxygen-modified samples were more hydrophilic than argon-modified samples. The AFM images showed that surface roughness increased with plasma treatment. The protein adsorption experiments carried out with single protein solutions demonstrated that the adsorption of bovine serum albumin and fibrinogen decreased drastically by increasing the applied power and exposure time of the glow discharge. A similar decrease in the adsorption of protein was also observed for human blood proteins. The alterations of the conformational structures of the adsorbed proteins were examined by fluorescence spectrophotometry. Similar spectra with the same maximum wavelength were observed for native and desorbed proteins. These results showed that no denaturation of the proteins occurred upon adsorption on the surfaces of the prepared membranes.