The spin-label method has been used to study the structure and molecular motion of polystyrene chains adsorbed on porous silica. Spin-labelled polystyrene (PS) with a narrow molecular weight distribution, having M-w (weight average molecular weight) = 1.9 x 10(5) was adsorbed on the surface of porous silica with two different pore diameters, 28.5 nm (MB-300) and 81.3 nm (MB-800), in cyclohexane (C6H12) and carbon tetrachloride (CCl4) solutions at 35 degrees C. E.s.r. spectra were observed at various temperatures after the samples were completely dried. The anisotropic hyperfine splitting due to nitrogen nucleus observed at -196 degrees C, which is a good measure of the magnitude of the PS-silica interaction, is larger for the adsorbed PS from the CCl4 solution and the PS on the silica with the larger pore diameter. The molecular mobility of the PS chains was estimated from temperature dependence of the e.s.r. spectra. It is found that the conformations of the PS chains in the Theta (C6H12) and good (CCl4) solvents affect the structures of adsorbed PS on the silica surface and the molecular mobility decreases with increasing PS-silica interaction.