Surface modification of precipitated carbonate-silicate fillers was performed. For this purpose silane coupling agents and stearic acid were used. The modification was performed employing two agents: silane, with affinity to silicate silanol groups, and stearic acid, adsorbing on the carbonate surface. The unmodified and the modified carbonate-silicate fillers were subjected to physicochemical analysis. Studies were also performed which aimed at determining dispersion and particle morphology using SEM and DLS techniques. Moreover, calorimetry permitted to establish the extent of hydrophobization of carbonate-silicate filler surface following the modification. The extent of hydrophobization of filler surface clearly correlated with the uniform character of particles formed in the course of surface modification.