Abstract: Distillers grains,one of the lignocellulosic biomasses riched in cellulose and hemicellulose,was used as an economically attractive carbohydrate feedstock for production of lactic acid by saccharification and microbial fermentation processes. The aim of this study was to investigate the possibility of lactic acid production from distillers grains hydrolysates by the mutant strain Rhizopus oryzae LS-1 and to optimize the biological conversion of reducing sugars into lactic acid to evaluate the culture conditions. The effects of factors such as inoculations size,Ca CO3 addition,p H value and fermentation time on the lactic acid concentration and the reducing sugars utilization rate were researched by the method of orthogonal experimental design.In addition,the sugar metabolism of R.oryzae LS- 1 was also studied. The results show that R. oryzae LS- 1 has the capability to utilize xylose or glucose as carbon resource,furthermore there are synergic and complementary actions during the coexistence of both sugars. The cooperated operations of metabolism was beneficial to the bioconversion of lignocellulosic biomass for lactic acid production. Fermentation results show that ammonium chloride is the most favorable nitrogen source for lactic acid production,the optimal fermentation conditions are inoculation size of 3.0% seed culture,Ca CO3 addition of 80g·L- 1,fermentation time of 96 h and culture p H of 6.5. Under optimal conditions,13.27 g / L lactic acid was produced and the sugar conversion rate reached 79.61%. This study provided an encouraging means of producing lactic acid from lignocellulosic resource such as the low- cost distillers grains. It was concluded that the fermentation technics for the production of lactic acid from distiller grains was worthy to be developed on a large scale.