Time-resolved small-angle X-ray, scattering (SAXS) investigations were carried out in order to clarify the heat treatment effects on the structure of a dehydrated substance made from a crystalline-polymer (poly(vinyl alcohol)) hydrogel. The heat-treatments performed in the present studs consisted of two procedures: an initial temperature increase to a target temperature (T-t) and a successive thermoregulation to maintain T-t. The evolution of the SAXS profile in the first procedure indicated that a mesoscopic structure, which probably originated from an inhomogeneity between crystalline and amorphous ingredients, began to develop around the g-lass transition temperature and became more distinct and large with increasing temperature, However, the SAXS profile showed almost no change for a long time during the second procedure. The latter feature was quite different front the crystallization processes of polymers without cross-linkage. which demonstrates how the cross-linkage hinders the thermal motion of the network polymers in the dehydrated gel.