Density (r), viscosity (h) and ultrasonic velocity (U) of L-threonine, L-leucine and L-histidine in water and aqueous tetraethylammonium bromide (0, 0.05 and 0.1 mol?dm–3) have been measured at 303.15K. These measurements have been used to calculate some important parameters viz., adiabatic compressibility (b), molar hydration number (nH), apparent molar compressibility (), apparent molar volume (), limiting apparent molar compressibility (jV0) and their constants (,) and transfer volume (). The viscosity data have been analysed on the basis of the Jones-Dole equation, the viscosity A and B coefficients have been evaluated. The variation of these parameters with concentrations clearly suggests the role of alkyl cation on the ion-solvent interactions in aqueous medium. The structural influence of the large cations of quaternary ammonium salts upon solvent is also taken into consideration.