The adsorption process of albumin, lysozyme and lactoferrin was investigated onto polymer surfaces, both hydrophobic and hydrophilic treated by oxygen-plasma. In particular thin films of polyhydroxymethylsiloxane (about 90 degrees of static water contact angle) were converted by oxygen plasma treatments at reduced pressure into hydrophilic SiO(x) phases (less than 10 degrees of water contact angle). The protein adsorption process was investigated in situ by quartz crystal microbalance with dissipation monitoring in terms of coverage and kinetics mechanism, while chemical structure and topography of the protein adlayers were studied ex situ by angular-resolved XPS and atomic force microscopy, respectively. The plasma surface modification of the polymer film drastically modified the adsorption process of the three proteins, both in terms of kinetics and coverage.