The density of poly(N-vinylimidazole) dilute solutions in methanol, triethylene glycol, dimethyl sulfoxide, and N,N-dimethylformamide as well as in an aqueous neutral (with and without ionic strength) and acid solution have been measured at several temperatures. The specific volume of the polymer in bulk has been determined experimentally and theoretically, following the group aditivity method, and both values were coincident. Partial specific volume and thermal expansion coefficient were found to be solvent-dependent. These results were interpreted in terms of the different types of solvation or the interaction of polymer-solvent.