A genetically engineered Lactobacillus plantarum mutant was applied for the production of D-lactic acid from corncobs by simultaneous saccharification and fermentation (SSF). Using a corncob hydrolysate obtained by a combination of dilute acid treatment using 1.5% H2SO4 followed by enzymatic saccharification, the L. plantarum mutant completely assimilated both glucose and xylose in the corncob hydrolysate within 20 hours, resulting in the successful production of D-lactic acid with high optical purity in a batch culture. To improve the performance of D-lactic acid production from corncobs, SSF experiments from 100 to 250 g/L of acid-hydrolyzed corncobs using 1.5% H2SO4 were performed, and 49.7 to 101 g/L of D-lactic acid with 96.8-98.6% of optical purity was successfully produced.