The main object of this research was to determine the optimum lactose concentration for ethanol production from whey by using two yeast strains of Kluyveromyces lactis NRRL-Y-1140 and Kluyveromyces lactis H-8583. The optimum lactose concentration was determined by fermenting whey powder solutions with different lactose concentrations (5%, 10%, 15%, 20%) at pH and 30 ^oC. It was seen that the yeasts mentioned above fermented the whey solution containing 5% lactose, with ethanol yield of 80%, in 100 hours. It has been observed that yeast strains employed in this study could not complete the fermentation of whey solution containing higher than 5% lactose, even in 170 hours.