Particulate-filled composites were prepared from CaCO(3) and polymer matrices of various acid-base characters. Interfacial interaction of the components was characterized by the reversible work of adhesion, which was calculated either from dipole-dipole or acid-base interactions. The thickness of the spontaneously formed interlayer was derived from the tensile strength of the composites. The results proved that acid-base interactions play an important role in interphase formation. The strength of interfacial adhesion is determined by the joint effect of dispersion forces and acid-base interactions. Stronger interaction leads to a thicker interphase with decreased mobility. Treatment of CaCO(3) with an aliphatic fatty acid leads to a decrease in the strength of interaction, and to changes both in the thickness and properties of the interphase. In composites containing coated fillers, acid-base interactions influence composite properties less due to the neutral character of the surface.