Poly(N-Vinyl 2-pyrrolidone-g-tartaric acid), PVP-g-TA hydrogels were prepared by gamma-irradiating ternary mixture of VP/TA/Water. The influence of pH, temperature mid ionic strength of swelling media on the equilibrium swelling properties of these hydrogels was investigated. Typical pH and temperature responses mere observed by hydrogels such as high pH and low temperature swelling mid low pH and high temperature deswelling. A change in the ionic strength of the swelling solution from 0.01 to 0.2 caused a decrease in equilibrium degree of swelling hydrogels. The average molecular weight between cross-links, (M) over bar (c), mid polymer - solvent interaction parameter, chi of PVP-g-TA hydrogels were determined according to equation recently derived by Sen and Guven for the swelling behavior of charged polymeric network. Copyright (C) 2002 John Wiley Sons, Ltd.