A new experimental technique which allows determination of viscoelastic properties of thin polymer films with thickness of the order of micrometers and below is presented. The method consists of sandwiching the polymer film between two metal electrodes and detecting the periodic deformation due to an alternating electric held applied between the electrodes. A Nomarski optical interferometer was used to record the thickness changes of the order of nanometers. Exemplary results are presented for a 2.1 mu m thick film of poly(methyl methacrylate). Both temperature and frequency dependencies have been determined. The analysis of the electromechanical data yielded both the real and imaginary parts of the compressibility of the thin film. The softening of the polymer around the glass transition temperature could be clearly resolved. The comparison to the bulk moduli yielded the temperature dependence of Poisson’s ratio. Relaxation times deduced from electromechanical experiments at temperatures from 30 to 150 degrees C and frequencies between 80 Hz and 32 kHz agreed well with those determined by bulk mechanical and dielectric spectroscopy.