Young's modulus of coat films has been estimated by using the double-beam vibration-reed method. The 18-8 stainless steel (SUS304; JIS) sheets coated by some inorganic films were prepared by using the sputtering and CVD. The method are applied to estimate the modulus by using the fundamental mode resonant frequencies of coated substrate before and after deposition of the films. The resonant frequency of each sample was measured by shaking the sample, and the displacement response detected by the eddy current displacement sensor. The specimens include non-coated stainless, TiO2, CrN, TiN, and diamond-like carbon(DLC) coated sheets. The thickness of the coat films range from 0.4 to 3.5. The non-coated substrate specimen requires an adequate annealing corresponding to the thermal history of the film deposition. The measured resonant frequencies have some amplitude dependencies, therefore the frequencies were extrapolated to zero amplitude. The extrapolated frequencies, the modulus of the annealed substrate, density and the geometrical parameters were assigned to the formula of the resonant frequency for the double-beam. The measured modulus of SUS304 substrate, TiO2 and TiN films are smaller than bulk form. The measured modulus for the CrN film is larger than the one form the literature data. The modulus of DLC film falls onto the range of literatures.