The state of absorbed water in polyamide 6 elongated to several levels have been investigated in relation to the polymer microstructure. The absorption behavior of distilled water at 20 degrees C was monitored until the saturation. Both the diffusion coefficient and the equilibrium content of water were increased by plastic elongation. The large elongation caused a reduction in the storage modulus and rises in the loss tangents for alpha- and beta-relaxations. The DSC measurements clearly indicated several exothermic peaks showing the presence of freezable bound water in the largely elongated specimen. These results suggest that some microstructural defects like voids are formed by the collapse of crystals by large elongation, and the water molecules are accumulated in such defects under weaker interaction with the surrounding polymer. Supposing the pore as the structural defect, the pore size distribution was obtained from the DSC curve by the method of thermoporosimetry. Assuming the cylindrical pores, they were characterized to have the total volume of about 13.5 x 10(-4) mm(3) g(-1), the surface area of about 1.1 m(2) g(-1), and the average radius of about 2.5 nm, being appropriately called mesopore. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1272-1277, 2010