Sugar beet pulp (SBP) contains more than 40% carbohydrate and less than 2% lignin; therefore, it could be a promising feedstock for bioethanol and other biofuel production without severe pretreatment. In this research, the ensilage process was studied for storage and pretreatment of SBP for the purpose of sustainable ethanol production. Two lactic acid bacteria (LAB) strains, including Lactobacillus brevis B-1836 (LAB #120) and Lactobacillus fermentum NRRL B-4524 (LAB #137) were used to ensile SBP in 1L reactors at 26°C for 90 days. The effects of LAB loading level and SBP packing density were investigated using response surface methodology. Ensilage without LAB inoculation was conducted as a control. The ensiled SBP was hydrolyzed with commercial cellulases to study the effect of ensilage on the enzymatic digestibility of SBP. A particularly interesting finding was that the ensilage process had a pretreatment effect on the SBP. Enzymatic digestibility of SBP was increased by 4-35% for inoculated treatments and 20-30% for the controls, compared to untreated SBP. The improvement in enzymatic digestibility of SBP could be due to pectin and hemicellulose removal and/or cell wall structural changes caused by microbial activity during the ensiling process.  Therefore, the ensilage process could be a suitable biological pretreatment method for SBP. Inoculation with LAB strain #137 tended to have the most positive effect on enzymatic digestibility of SBP with the lowest losses of hemicellulose and cellulose.  Performance of this strain depended on packing density and level of inoculation.