Four kinds of colloidal silica particles with different size (27, 58, 79 and 173 nm respectively) were synthesized by sol-gel process and modified with 3-glycidoxypropyltrimethoxysilicane, then homogenously dispersed into the epoxy resin and cured with alicyclic amine on aluminum alloy substrates. The results showed that the Si-O-Al bond was formed at nanocomposite coat/substrate interface, introducing nanosilica significantly enhanced the adhesive strength, scratch resistance, abrasion resistance and corrosion resistance of coats, but different particle sizes of nanosilica had various impact on these properties, which seemed to be related to the structure of the silica surface. (c) 2005 Springer Science + Business Media, Inc.