A method for calculation the elastic constants of a composite, including polymer matrix, fully exfoliated layered nanoparticles and non-exfoliated particles is considered. Exfoliation degree has been introduced to characterize the extent of exfoliated filler particles. It has been demonstrated that linear growth of the modulus of elasticity is predicted by increasing the nanofiller content in the polymer matrix, whereas greater values of the modulus are expected at higher exfoliation degrees. However, growth of the modulus of elasticity is non-linear if degree of exfoliation is changed. Consequently, it is possible to estimate slow-down in the rate of the modulus increase due to agglomeration of the particles, especially at higher nanofiller concentrations in the polymer matrix. Validation of the developed approach for prediction of elastic constants if performed and it is concluded that the proposed model approximates the change of the modulus of elasticity of polymer composite reinforced with nanostructured layered silicates by considering concentration of the nanofiller as well as its distribution pattern within the polymer matrix.