A positron-annihilation lifetime technique was applied to four kinds of epoxy resin (cresol novolac, tris-hydroxy-phenyl-methane (THPM), tetra-methyl-biphenol and bis-phenol A) in order to study the relation between the intermolecular-space holes and water absorption. The sizes of the holes were measured, based on the life-time (tau(3)) of the ortho-positronium. Since THPM has a larger tau(3) value (hence, a larger intermolecular-space hole) and absorption rate than that of the other samples, a correlation between tau(3) and the absorption rate has been shown to be evident. Assuming a very simplified model, the shapes of the holes for the smallest unit cell were calculated using a computer code of molecular dynamics; the shape for THPM was found to be different from those of the other three samples.