The aim of this study was to investigate succinic acid production from lactose concentrate, a by-product of cheese-making, using Actinobacillus succinogenes and Basfia succiniciproducens. Although the capability of these strains to metabolize different sugars is already known, their application in the conversion of lactose bears high potential for optimization. With regard to B. succiniciproducens this approach is completely novel. In particular the influence of the mediums sugar concentration and its supplementation with yeast extract to prevent a lack of proteins and vitamins were examined. Lactose based media containing sugar concentrations between 20 and 65 g L-1 and 5 g L-1 yeast extract were fermented, whereby both strains showed comparable performances. The best results in succinic acid yield and acid concentration, 0.57 g g-1 initial sugar and 23 g L1, were achieved at an initial sugar concentration of 43 g L-1. The necessity of yeast extract was demonstrated using the sugar optimized medium without supplementation. As a result, yield and concentration of succinic acid dropped to 0.34 g g-1 and 13 g L-1, the sugar consumption decreased from more than 99 to less than 55 %. Therefore the supplementation amount of 5 g L-1 yeast extract can be regarded as well-balanced.