EPR spectroscopy of labeled poly(ethylene oxide) (PEO) grafted on silica has been used to characterize the conformation and local dynamics of the chains. Grafted molecules of MW 2000 with grafting ratios of 0.045, 0.057, 0.126, and 0.42 molecules/nm(2) were in contact with benzene. The mobility of the label was compared with that observed for solution of PEO from very diluted to highly concentrated and even bulk PEG. Thus, the concentration inside the grafted layer could be evaluated and also the thickness, which evolves rather linearly with the grafting ratio.