Medical polyurethane was treated with 20 keV nitrogen ions with a fluence of 1014–1016 ions/cm2. The modified polyurethane has a layered structure consisting of a 70-nm carbonized layer and a partly depolymerized layer below the carbonized layer. The high level of activity of the polyurethane due to free radicals provides stable adhesion of protein molecules to the surface layer of the polyurethane. The high level of hydrophilicity of the modified polyurethane surface preserves the biological activity of the attached proteins. This contributes to the attachment of endothelial cells to the polyurethane surface and their proliferation. Thus, this modified polyurethane can be used as a material for soft-tissue medical implants.