The adsorption of proteins on surfaces with grafted polymers is studied using a molecular mean-field theory. The effects of changing the protein-surface interactions, the polymer-surface interactions, the polymer segment volume, and the type of possible protein conformations adsorbed are studied. The main results of these studies are for the equilibrium amount of protein adsorbed; however, the theory also enables the study of the conditions that determine the kinetics in the initial stages of the adsorption process. The amount of protein adsorbed on the surfaces with grafted polymers depends on the surface density of polymer, the protein-surface interaction, the polymer-surface interaction, the size of the polymer segments, and the ability of the proteins to undergo conformational changes upon adsorption. The proper choice of polymers used can lead to the specific adsorption of a given type of protein conformer. One of the main conclusions from this study is that protein adsorption is very sensitive to the details of the surface modifiers. For example, contrary to intuition, increasing the size of the polymer segments may result in an increase of the amount of protein adsorbed at fixed polymer surface coverage. The dependence of the adsorption of proteins on grafted polymer molecular weight depends on the interactions between the polymer and the surface. It is found that for model polymers mimicking poly(ethylene oxide), in terms of the monomer size and the bare ethylene oxide hydrophobic surface interactions, the adsorption of proteins is usually found to be at the crossover between two different regimes. The results presented here suggest what kind of polymers may be optimal for prevention of protein adsorption depending upon the type of surface.