This paper proposes a quasistatic method for Poisson’s ratio estimation of isotropic acoustical porous materials. The method is based on longitudinal and transverse displacements measurements of a cylindrical sample of the material under study, this sample being submitted to an harmonic and uni-axial compression. At the same time, damping and stiffness of the material can be measured, as the sample reaction force and vertical displacement are also measured. For a given shape factor defined as the radius over twice the thickness of the sample, a polynomial relation between displacements ratio and Poisson’s ratio are used. The Poisson ratio is the solution for which the difference between the polynomial and the measured value is null. The method is validated numerically and applied to the Poisson’s ratio estimation of a melamine foam which is close to be isotropic.