Thermodynamics of the interaction between tetrazole-containing polyelectrolytes and water was studied at 298 K. The Gibbs free energies, enthalpies, and entropies of mixing are negative for the dissolution and swelling of poly(C-vinyltetrazoles) in water. For un-ionized polyacids the plots of the enthalpies of dilution (mixing) for un-ionized polyacids versus the composition of polymer-water system exhibit additional extrema at a water content 10-20%. This fact is explained by the ''ordering'' and the ''disorderings'' effects of water. The affinity of poly(C-vinyltetrazoles) to water is significantly enhanced on ionization of the polymers considered. The changes in the thermodynamic parameters of polymer dissolution depend on the conformational state of macromolecules, which is determined by their hydrophilic-hydrophobic balance.