The diffusion coefficients (D) for lactose and ethanol through calcium alginate gel beads were determined based on the mathematical approach of Pick's second law. Different experimental conditions were tested to evaluate the behavior of the diffusion coefficient of different concentrations of lactose and ethanol in Ca-alginate (3, 4, and 6) % at varying temperatures (298.15, 303.15, and 308.15) K. Results showed that diffusion coefficients were independent from the concentration of lactose and ethanol, as well as from the concentration of Ca-alginate. Diffusion coefficients were affected by temperature, increasing from 4.67.10(-10) m(2).s(-1) to 6.96.10(-10) m(2).s(-1) for lactose and from 1.46.10(-10) m(2).s(-1) to 2.68.10(-10) m(2).s(-1) for ethanol. These results can be used for the project and scaling up of immobilized bioreactors for the conversion of lactose into ethanol.