A new method for density and thickness measurements of a thin-film is proposed by a pressureof-flotation method (PFM). A density difference is determined by the PFM while a mass difference is measured by an electric balance for the samples before and after thin-film is prepared on a substrate (Fig). Then, the density and thickness of the thin-film on the substrate can be derived. The density and thickness of a molybdenum thin-film prepared on a silicon substrate are evaluated by this method. The estimated standard uncertainties of density and thickness for the molybdenum film are 3.8 % and 4.0 %, respectively.