Lactic acid is a product that finds several applications in food, cosmetic, pharmaceutical and chemical industries. The main objective of this work was the development of a bioprocess to produce L(+)-lactic acid using soybean vinasse as substrate. Among ten strains, Lactobacillus agilis LPB 56 was selected for fermentation, due to its ability to metabolize the complex oligosaccharides. Fermentation was conducted without need for supplementary inorganic nitrogen sources or yeast extract. Kinetic and yield parameters determined at laboratory scale were 0.864 and 0.0162 for Y-P/S and Y-X/S, 0.0145 g/L h (r(x)), 1.32 g/L h (r(s)) and 1.13 g/L h (r(p)). The use of vinasse enriched with soybean molasses provided higher lactic acid concentration (138 g/L), the best proportion of inoculum being 25% (v/v). After scale-up to a pilot plant, kinetic and yield parameters were 0.849 and 0.0353 for Y-P/S and Y-X/S, 0.0278 g/L h (r(x)), 0.915 g/L h (r(s)) and 0.863 g/L h (r(p)). (C) 2010 Published by Elsevier Ltd.