Purpose. To analyze the influence of structural and morphological, and elastic characteristics of defects on the features of the structure and deformation of some sandstones based on the modeling approach and interpretation of experimental data of velocity of longitudinal and transverse acoustic waves. Methodology. We have involved a series of experimental studies of density, porosity, and determination of the velocity of propagation of longitudinal and transverse acoustic waves in samples of sandstone with different structural organization. Findings. The elastic parameters of defects of solid structure were calculated based on the velocities of propagation of acoustic waves for sandstones with different effective Poisson's ratio. The normal and tangential compliances with the effective Poisson's ratio of sandstone were comparatively analyzed. Poisson's ratio of the medium matrix was calculated based on the variations of the velocities of propagation of acoustic waves under the influence of external pressure. Originality. The deformation behavior of sandstones was considered on the basis of the model of microinhomogeneous medium as an elastic matrix and planar defects inclusions. Theoretical estimates of the parameters of defects, based on the elastic constants of linear elasticity theory, indicate the adequacy of the model to describe the strain state of imperfectly elastic rock. The possibility of the existence of negative Poisson's ratio in sandstones with high normal compressibility and the contribution of the contact interactions were theoretically justified. Practical value. Theoretical estimates of the parameters of defects, based on the elastic constants of linear elasticity theory, indicate the adequacy of the model to describe the strain state of imperfectly elastic rock. There were obtained the relations for evaluation of normal and tangential compliance on the basis of effective elastic moduli microinhomogeneous medium, elastic moduli and the Poisson's ratio of the matrix medium. It is shown that the concentrations of defects in their compliance and effective Poisson's ratio have an inverse relationship, which determines the strain-elastic properties of the medium of propagation of acoustic waves. [ABSTRACT FROM AUTHOR]