Densities , ρ, and viscosity, η, have been measured for ascorbic acid, thiamin HCl, nicotinic acid and pyridoxine HCl have been measured in water and in aqueous sodium chloride solutions at (293.15, 298.15, 303.15 and 308.15) K. The apparent molar volumes were determined from the measured density data. These volumes were extrapolated to zero using suitable empirical or theoretical equations to determine the corresponding infinite dilution values. Ionization of the vitamins under studied were suppressed using sufficiently acidic solutions. Apparent molar volume at infinite dilution for all vitamins, were found to be increase with increasing temperature in acidic solution and the presence of co-solute NaCl. On the other hand, increasing the concentration of co-solute NaCl leads to decrease the apparent molar volumes. These results were interpreted in terms of complex vitaminswater- co-solute NaCl interactions. Apparent molar volumes of transfer at infinite dilution for vitamins from water solutions to NaCl solution at various temperatures in the range (293.15 – 308.15) K were calculated. The resulting data have been utilized to the effect of overlapping of the hydration co-spheres on net volume of vitamins. The viscosity data have been analyzed using Jones-Dole equation, and the derived parameters, Jones-Dole coefficient, B, and Falkenhagen coefficient, A, were interpreted in terms of solute-solvent and solute-solute interactions respectively, for ascorbic acid, thiamin HCl, nicotinic acid and pyridoxine HCl. The variation of B coefficient with temperature, (dB/dT), have been also calculated for vitamin solutions, and the obtained data was interpreted on the basis of the structure-making and structure-breaking behavior. Free energy of activation of viscous flow per mole of solvent, Δμ1°, and solute, Δμ2°, were obtained by application of the transition–state theory to the B coefficient data and the corresponding activation enthalpy, ΔH0, and entropy of activation, ΔS0, of viscous flow were also determined for vitamins.