The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring-opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3-glycidoxypropyl trimethoxysilane. The alcohol-grafted silica played the role of a coinitiator/chain-transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.-% of a hairy layer of grafted PEO chains were successfully produced by this technique.