The effects of hygrothermal aging history and initial water content on sorption behavior and the physical properties of a commercial particle-filled epoxy-based adhesive were studied by the analysis of the water reabsorption process. ATR-FTIR analysis was performed to characterize the hydrogen bond interactions among the water and either resin or fillers. Swelling behavior and the depression of the glass transition temperature (T-g) under different hygrothermal aging histories were related to the water in the apparent free volume of the adhesive. The results show that the water diffusion of the adhesive is a non-Fickian process. It is also observed that swelling (which is reversible and consistent with hydrogen bond formation) and the rate of diffusion are not only dependent on the hygrothermal temperature but also the hygrothermal history. In addition, the swelling observed on the reabsorption process does not alter the apparent free volume of this adhesive system, and T-g depression is independent of the final equilibrium water content of the system.