The diffusion coefficients are very important for explaining the heat and mass transfer phenomena in agricultural products and can be used in thin-layer equations for computer simulations of designing new and improving existing commercial drying and re-wetting process. Thin-layer moisture adsorption data were measured for barley in the temperature range of 5.7 to 47.3°C and for relative humidities between 48.2 and 88.6% to determine the diffusion coefficient. The initial moisture contents were in the range of 10.15 to 11.55% dry-basis. New equations, exponential and arrhenius-type, for temperature dependent liquid diffusion coefficients in re-wetting barley are presented. The diffusion coefficient in rewetting barely was lower than that in drying. The results presented here, over five day re-wetting, will be useful in studying the long term moisture transf3r process occurring during cooling and ventilated stored barley.