New covalent bonded polymer-calcium silicate hydrate (C-S-H) composites were prepared. For this purpose, two sets of hydrosoluble copolymers, both containing trialkoxysilane (T-silane) and/or methyldialkoxysilane (D-silane) functions, were synthesized. The addition of these polymers during the synthesis of C-S-H by the sol-gel method allowed us to obtain hybrid materials. The influence of different synthesis parameters, such as the silane content and the nature of the silane functions grafted to the polymer backbone, was studied. Characterisation of the composite materials by thermogravimetry and elemental analysis showed that chemical interaction of polymers and C-S-H is due only to the presence of T-silane functions. 29 Si CP MAS NMR analysis confirmed the existence of covalent linkages between the inorganic silicate chains of the C-S-H crystallites and the T-silane functions. The specific incorporation of these new classes of silane-modified polymers in C-S-H structure may be successfully used in the preparation of new polymer-cement composites with reinforced mechanical properties.