The methods of transverse and longitudinal surface waves and of oscillating barrier were used to measure a surface dynamic elasticity of poly(ethylene oxide) films spread on aqueous substrate within the frequency range of 0.001-520 Hz. Unlike the adsorption films, the main relaxation processes in the spread poly(ethylene oxide) films are observed at higher frequencies. A comparison of static and dynamic values of the surface elasticity shows that the surface film at surface polymer concentrations higher than 0.4 mg/m² cannot be considered already as purely two-dimensional film. It was found that the surface tension (surface pressure) can be insufficiently sensitive to conformational transformations in the surface polymer films.