Densities and heat capacities of lysozyme in Na-acetate buffer (pH 4.2) containing 0.64 m sodium chloride at 25C were determined by Anton Paar 60/602 digital densimeter and differential scanning adiabatic calorimeter DASM-4 in the range of lysozyme concentration 0.000499–0.002450 m. The measurements were made after 1, 24 and 48 h of the dissolution of lysozyme in the buffer. The changes of the values of apparent molar volumes and heat capacities in time were observed.