Disclosed is the biological production of lactic acid using a microorganism. A transformant capable of producing lactic acid of high optical purity at high yield, a method for the preparation thereof, and a method for producing lactic acid in a convenient and economically beneficial manner using the same are provided. The Zymomonas mobilis transformant can produce lactic acid of high optical purity at high yield without a stringent limitation to production conditions and a regulation of the intracellular metabolism pathway. Because it requires no additional separation and purification steps, the use of the transformant allows the production of lactic acid in a short process, resulting in a significant reduction in production cost, and avoiding the environment problems caused by precipitate wastes, which brings about environmental issues.