Nanoscale topography was constructed on a thermally responsive poly(N-isopropylacrylamide) (PNIPAAm) surface by grafting the polymer from silicon nanowire arrays via surface-initiated atom transfer radical polymerization. The as-prepared surface showed largely reduced platelet adhesion in vitro both below and above the lower critical solution temperature (LCST) of PNIPAAm (similar to 32 degrees C), while a smooth PNIPAAm surface exhibited antiadhesion to platelets only below the LCST. Contact angle and adhesive force measurements on oil droplets (1,2-dichloroethane) in water demonstrated that the nanoscale topography kept a relatively high ratio of water content on the as-prepared-surface and played a key role in largely reducing the adhesion of platelets; however, this effect did not exist on the smooth PNIPAAm surface. The results can be used to extend the applications of PNIPAAm in the fields of biomaterials and biomedicine under human physiological temperature and provide a new strategy for fabricating other blood-compatible materials.