Grafting of organosilane-functionalized substances onto the surface of nano-sized silica particles was studied by temperature-programmed oxidation (TPO), solid-state C-13 and Si-29 MAS NMR and DRIFT spectroscopy. By using Si-29 MAS NMR quantitative data on the proportions of the various grafted structures, grafting yields and the reactivity of the geminal and free silanols towards the coupling agent were obtained. For 3-(trimethoxysilyl)propylmethacrylate as coupling agent and 2 maleic acid as catalyst, the TPO weight loss of about 24 wt.% revealed a hypothetical coverage of about 5.5 graft/nm(2). Compared to the surface concentration of 2-3-OH groups per nm(2), this value can be only explained by grafting precondensed silane molecules onto nano-sized silica, assuming a core shell principle.