Propionic, acetic, and succinic acids have been selectively separated from their mixture obtained by P. acidipropionici fermentation using facilitated pertraction with tri-n-octylamine (TOA). This technique allows the recovery of acetic and succinic acids from the mixture, the feed phase raffinate containing only propionic acid. The pH-gradient between the feed and stripping phases, the carrier concentration in the liquid membrane, and the addition of 1-octanol control the selectivity of acids pertraction, with TOA concentration exhibiting the most important influence. In the absence of 1-octanol, at a pH-value of feed phase = 2, pH-value of stripping phase = 10, the maximum selectivity factor (S = 25) was reached for the carrier concentration 70 g L-1. By 1-octanol addition, at the same pH-values of the aqueous phases, the maximum selectivity factor (S = 19) was reached for lower carrier concentration, namely 50 g L-1. The reduction of the selectivity factor for the pertraction system containing 1-octanol is compensated by diminishing the material consumption required for separation.