The introduction of nanoscale features brings with it a high density of surface interface boundaries and effectively introduces an additional boundary material that exhibits properties different from the surrounding surfaces. We systematically varied the feature size of self-assembled polystyrene-block-poly(methyl methacrylate) copolymer nanopatterns from 13 to 200 am and demonstrated that the basic property of protein adsorption on a nanopatterned surface can be modulated by the length density of surface interfaces present. Protein adsorption on the nanopatterns could be described by a modified adsorption affinity along the surface interface with an effective width on the length-scale of individual proteins. Due to the intrinsic high density of surface interfaces in many polymeric thin film nanopatterns and structures, the interaction of proteins with such interfaces may be of particular relevance to cell-surface studies and to biomaterial and biosensor applications involving nanoscale features.