A moderately water-swollen hydrogel with molecularly-ordered aggregate structure was prepared by copolymerizing acrylic acid with the hydrophobic 16-acryloylhexadecanoic acid (AHA) and 12-acryloyldodecanoic acid (ADA). X-ray diffraction indicated that the swelling of the network occurs first by disordering of a layer structure and then by the elimination of side-chain crystallization. Changes in the degree of swelling are produced by either changes of pH or the addition of ethanol to the aqueous gel. The swelling data are consistent with the X-ray diffraction results.