Densities, r, viscosities, h, and refractive indices, n D of aqueous caffeine (0.5 M) and of solutions of amino acids, l-phenylalanine (Phe), l-tyrosine (Tyr) and l-histidine (His), (0.01-0.05 M) in aqueous-caffeine have been measured at 298.15, 303.15, 308.15 and 313.15 K. From these experimental data, ap-parent molar volume, f v , limiting partial molar volume, f v o and the slope, S v , transfer volume, f v tr o , , Falkenhagen coefficient, A, Jones-Dole coefficients, B, free energies of activation per mole of solvent, Dm 1 o # and per mole of solute, Dm 2 o # , enthalpy, DH * and entropy, DS * of activation of viscous flow, and molar re-fraction, R m were calculated. The results are interpreted from the point of view of solute-solvent and sol-ute-solute interactions in these systems. It has been observed that there exist strong solute-solvent and weak solute-solute interactions in these systems. Further, the solute-solvent interactions decrease, whereas solute-solute interactions increase with rise in temperature. It is observed that these amino acids act as structure-makers in aqueous-caffeine solvent. The thermodynamics of viscous flow have also been discussed.