Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SRK2SO4 > SRKCl and SRNa2SO4 > SRNaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non-Fickian behavior in alkaline media. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3161-3167, 2010