Epoxy coatings were designed to give a hydrophobic property on its surface by modifying it with two kinds of amino substituted polydimethylsiloxane, and then effects of the modification on the structure, surface hydrophobic tendency, water transport behavior and hence corrosion protectiveness of the modified epoxy coatings were examined using FT-IR spectroscopy, hygrothermal cyclic test, and impedance test. The phase separation tendency is more appreciable when modified by amino branched polydimethylsiloxane (ABP) then amino terminated polydimethylsiloxane (ATP). In the results of EIS, the corrosion protection of epoxy modified coating by ABP shows better than epoxy modified coating by ATP. It was well agreed with its water transport behavior and hydrophobic tendency. (C) 2008 Elsevier Ltd. All rights reserved.