In order to facilitate its incorporation into a polymer matrix (mostly hydrophobic), calcium carbonate (CaCO 3 ), which is strongly hydrophilic, has to be chemically treated to avoid the formation of aggregates and to improve the compatibility with the polymer. The objective of this study is to analyze, by using contact angle measurements and X-ray photoelectron spectroscopy (XPS), the CaCO 3 surface after a chemical surface treatment with ethyltrimethoxysilane (ETMO) and polyphosphoric acid (PPA) in an organic solvent, in order to verify if these molecules are able to interact with the CaCO 3 surface, and to propose some hypothesis about the surface grafting mechanism. After several solvent washings were performed to remove all species in excess, contact angle results have pointed out the presence of an organic layer after the chemical treatment of CaCO 3 with ETMO and PPA. Based on XPS results, we propose a grafting mechanism of silane and phosphoric acid molecules. Ethyltrimethoxysilane induce an hydrolysis process of the CaCO 3 surface which leads to a condensation phenomenon. This SiOH network is adsorbed through hydrogen interactions with some hydroxyl groups. In the case of phosphoric acid, the molecules are adsorbed on carbon atoms through POC bonds formation. This original grafting points out the major role of the solvent nature with CaCO 3 surface reactivity.