The rheological behavior of thin polymer layers in composite materials could depend on the layer thickness and on the substrate surface properties. Therefore, mechanical characterization of the bulk polymeric materials is not sufficient to predict the behivior of adhesive layers between substrate. Measurements in the glass transition region of polymer layers of up to 10 µm thickness require a measuring device with a high stiffness of the clamping device. Because of small deformation amplitudes in the linear range, high sensitivity for the two measured parameters force and displacement is required. Previous investigations of different adhesive films between polymers demonstrate the potential of the DMA 861e (Mettler-Toledo) for such applications. With this instrument the dependence of the rheological properties on the thickness of a PU-adhesive between metallic substrate was measured at thicknesses from 50 µm to 500 µm in a frequency range between 0.1 Hz and 100 Hz we used. The results show an increase of the glass transition temperature and the modulus in the rubbery range with decreasing the layer thickness.