Diffusion coefficients were: determined for benzene, toluene, ethylbenzene, p-xylene, o-xylene, 1, 3, 5-trimethylbenzene in n-heptane and in n-octane at 303.2K to 333.2K. A new predictive equation for liquid diffusion coefficients, based on Eyring＇s absolute rate theory, was proposed. The active energy of diffusion was determined from the active energy of viscosity. It had the advantage of being based entirely on theoretical considerations and involved no experimental curve-fitting parameters.