The effects of nonprotein polymers on the water-swelling properties of fish protein-based hydrogel were studied. Inclusion of carboxymethyl cellulose (CMC), poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA), or guar gum at a 2.5%, (w/w) level in an 80% ethylenediaminetetraacetic dianhydide (EDTAD)-modified fish protein hydrogel (10% monomer concentration) significantly decreased the extent of water uptake of the hydrogel. Among these polymers, PVA exhibited the greatest inhibitory effect. The inhibitory effect of these polymers on the water uptake of fish protein hydrogel was apparently due to the thermodynamic incompatibility of these polymers with the fish protein gel network and the consequent effect on the extent of relaxation of the crosslinked polypeptide network. In contrast, inclusion of 60% EDTAD-modified soy protein up to a level of 4% of the total protein in the gel did not affect the extent of the equilibrium water uptake of the gel. At higher levels, however, soy protein also decreased the amount of water uptake by the gel.