Epoxy resins are attractive materials for many engineering applications. However, they are susceptible to the moisture environment and can be degraded by the moisture. The moisture diffusion characterizations, which include weight changes, diffusion coefficients and the activation energy, have been investigated. The experimental results show that the desorption process from highly moisture-saturation tended to leave a small residual moisture content, which could only be removed by heating at relative high temperature. The further interpretation of this phenomenon is given from the activation of bound waters, by experiments and molecular dynamics simulations. (c) 2005 Elsevier B.V. All rights reserved.