Hydrogels based on n-alkyl methacrylate esters (n-AMA), acrylic acid, and acrylamide crosslinked with 4,4'-di(methacryloylamino)azobenzene were prepared. Swelling behavior of the hydrogels was studied by the immersion of slabs in buffered solutions at pH 2.2-7.4. The diffusion of water into the slabs was discussed on the stress relaxation model of polymer chains. The results obtained are in good agreement with Schott's second-order diffusion kinetics. The constants A and B of Schott's kinetics equation depend on the balance of hydrophobicity/hydrophilicity, the rigidity/flexibility, and the degree of crosslinking. The factors that exert the greatest influence on the swelling behavior of the gels include the degree of crosslinking, the lengths of the n-AMA side chains, and pH values. By adjusting these factors, the degree of swelling of the hydrogels in the small intestine can be controlled, and consequently the drugs may avoid being released before arriving in the colon.