Organic–inorganic hybrid core-shell nanoparticles with diameters ranging from 100 to 1000 nm were prepared by a one-pot synthesis based on base catalyzed sol–gel reactions using tetraethoxysilane and a triethoxysilane-terminated polyethyl- ene-b-poly(ethylene glycol) as reactants. Data from TEM, TGA, and solid-state NMR analysis are in agreement with the formation of core-shell nanoparticles with an inor- ganic-rich core and an external shell consisting of an amphiphilic block copolymer monolayer. The influence of the organic–inorganic ratio, solution concentration, and postcuring temperature on core and shell dimensions of the nanospheres were inves- tigated by TEM microscopy.