Adsorption of (gamma-aminopropyl)triethoxysilane (APS) on silica from aqueous solution was studied in situ by determining the differential enthalpies of displacement (microcalorimetry) and the adsorption isotherms (chromatographic type procedure). It is shown that, in the low concentration range (less than 0.2% in weight), the ethanol produced from the hydrolysis of the silane is not adsorbed whereas silanetriol (the other product of the hydrolysis) does not form polycondensates. The major role of the amino function in adsorption is demonstrated by the similar behavior of APS and of a much Simpler aminated molecule, i.e. propylamine. This similarity is seen from both the microcalorimetric results and the influence of pH on adsorption. Nevertheless, the partial irreversibility of APS adsorption (evidenced here by liquid flow microcalorimetry and not observed for propylamine) seems to show and measure the role of siloxane bonds in the adsorption of APS on silica.