Mechanical properties of polymeric matrix composites depend not only on the properties of the matrix, filler and their shares in the material, but on the characteristics of the matrix in thin layers close to the filler surface (interphase layer). Because of specific interactions of macromolecules with the filler surface, the interphase layer, as a rule, has a complicated microstructure. In some cases, the peculiarities of interphase layer play an essential role in formation of macroscopic mechanical properties of composite. In this work, based on the model approach, we propose a description of elastic properties of polymeric matrix composites in accounting for interphase layer properties. We present the estimations of the influence of molecular and structural characteristics of interphase layer on the mechanical properties of composite, and determine the variation intervals within which it is necessary to take into account the influence of interphase layer on the mechanical properties of a composite.