The spin-label method was used to study the structure and molecular motion of polystyrene (PS) chains adsorbed on a silica-tethered poly(ethylene oxide) (PEG). Spin-labelled polystyrene with a narrow molecular weight distribution, having a weight-average molecular weight (<(M)over bar (w)>) of 9.64 x 10(4), was adsorbed on the surface of the silica-tethered PEO with various grafting ratio lower than 2.1% in carbon tetrachloride solution at 35 degrees C. Electron spin resonance (e.s.r.) spectra were observed at various temperatures after the samples had been dried completely.The e.s.r. spectra observed at -196 degrees C were composed of two spectra arising from spin labels attached to ＇train＇ and ＇loop＇ (or ＇tail＇) segments, which were strongly and weakly interacted with the silica surface, respectively. The fractional amount of the ＇loop＇ or ＇tail＇ segments increases dramatically with grafting ratio of the PEG. The transition temperature of molecular motion estimated from the temperature dependence of the e.s.r. spectra decreases also dramatically with the grafting ratio of PEG. The ＇loop＇ or ＇tail＇ segments are attributed to PS chains protruding from the silica surface and/or embedded in the tethered PEO chains, whereas the ＇train＇ segments are trapped near the silica surface.