In this report the temperature dependence of the coefficient of electronic polarizability (phi (i)) is determined by means of the thermal expansion coefficient (beta) and ordinary/extraordinary refractive indexes measurements near the calamitic nematic-isotropic phase transition in a lyotropic mixture of sodium decylsulphonate, decanol, and water. These parameters (phi (i) and beta) were related to the extraordinary and ordinary refractive indexes via the temperature derivative of the Vuks's equation. The results showed that near the nematic-isotropic phase transition, the measured value of phi (i) was found to be about two orders of magnitude smaller than that obtained for thermotropic, showing a remarkable difference in the molecular electronic polarizability strength between lyotropic and thermotropic liquid crystals.6461