The excellent properties of the composites distinctly depend on the filler particles dispersion, which has close relationship with the surface treatment of filler particles. To improve the compatibility between the filler particles and the matrix, the surface of filler particles is generally treated with coating agents, which can be classified as "dispersants" and "coupling agents." Coating calcite (CaCO3) with dispersants is called a nonreactive treatment. The surface modification of CaCO3 with coupling agents is called reactive treatment. In this study, physical, chemical, morphological, rheological, and mechanical analyses were conducted to determine the effect of reactive and nonreactive surface treatment agents on the dispersion of CaCO3 in polypropylene/CaCO3 composites. Both agents successfully made the surface of CaCO3 hydrophobic. The results of this study revealed that, although stearic acid (SA) establishes stronger bonds with the calcite surface, isopropyl tristearyl titanate, unlike SA, improves the properties of the final product composite, which forms a bond at the polymer/filler interface.