The apparent molar volumes (V-m,V-2) and relative viscosities (eta(r)) at T = (298.15 and 308.15) K have been obtained for glycine, DL-alpha-alanine, and DL-alpha-amino-n-butyric acid in aqueous sodium caproate solutions from measurements of density and the flow time. The standard partial molar volumes (V(m,2)degrees), standard volumes of transfer (Delta(t)Vdegrees), the viscosity B-coefficients, and the activation thermodynamic quantities (Deltamu(2)(degreesnot equal) and DeltaS(2)(degreesnot equal)) of viscous flow have been calculated for the amino acids. It is shown that the standard partial molar volumes, viscosity B-coefficients, and activation free energies for viscous flow increase with increasing number of carbon atoms in the alkyl chain of the amino acids. An increase in V-m,V-2degrees and Delta(t)Vdegrees with increasing electrolyte concentrations have been explained due to the interactions of sodium caproate with the charged center of zwitterions for the amino acids. A comparison of the V(m,2)degrees values for glycine, DL-alpha-alanine, and DL-alpha-amino-n-butyric acid in different aqueous salts solutions showed that carboxylate ions have stronger interactions with amino acid than chloride, thiocyanate, and nitrate ions. Results of viscosity are discussed in terms of changes in solvent structure. (C) 2004 Elsevier Ltd. All rights reserved.