Densities and conductivity data for the sodium butyrate-glycyl dipeptide (glycylglycine, glycyl-L-valine, glycyl-L-leucine)-water systems were determined at 298.15 K. These data have been used to calculate apparent molar volumes of the dipeptides and limiting molar conductivity (Lambda(o)) of sodium butyrate. The standard partial molar volumes (V(2,phi)degrees), standard partial molar volumes of transfer for dipeptide from water to aqueous sodium butyrate solutions (Delta(t)V degrees), the hydration number, and volumetric interaction coefficients have been calculated. An increase in the transfer volumes and a decrease in hydration number of the dipeptide with increasing sodium butyrate concentrations have been explained due to stronger interactions of sodium butyrate with the charged center and glycyl unit of the peptide compared to the sodium butyrate-nonpolar group in peptide interactions. Using the V(2,phi)degrees values of the amino acids and an additivity relationship, the standard partial molar volumes of the peptides were estimated. The decrease in Lambda(o) with an increase in dipeptide concentration is attributed to the interaction of sodium butyrate with the dipeptides and the friction resistance of the solvent medium.