The extraction equilibria of aliphatic dicarboxylic acids with solutions of trialkylamine (TAA) in binary diluents were measured and compared. Oxalic, succinic, DL-malic and D-tartaric acids were used. Trialkylamine with C-7-C-9 carbon atom chains was dissolved in 1-octanol, methyl-isobutyl ketone (MIBK), and chloroform, or in their binary mixtures with n-heptane. Physical extraction with pure active diluents also was measured. The contribution of physical extraction was significant only in the case of succinic and oxalic acids and with octanol-1 and MIBK as diluents. In all systems, formation of the (1:1) acid: amine complex was found dominant at low aqueous-phase equilibrium acid concentrations. The values of the respective equilibrium constants grew in the same order as the first dissociation constants of these acids. In the region of high acid concentrations, overloading of amine was observed, indicating formation of (2:1) and (3:1) complexes. Here, the extraction grew with increasing lyophilicity of the acids. Various modifications of a mathematical model, incorporating reactions of formation of these complexes and physical extraction, were used for correlating the equilibrium data.