On the base of investigation of the thermomechanical properties of epoxy composites filled with nano-dispersed diamond and amine-diamonds on its base, it has been ascertained, that usage of modificated diamond with amine-groups in its surface layer, as filler of epoxy polymer, improves the properties of filled composites. It has been indicated that the influence of constant magnetic field is displayed in the decreasing of relative deformation on the same degrees of filling for the all examined compositions.