The phase diagram of the water + trans-aconitic acid + tributyl phosphate ternary system was obtained at 303.15 K. Experiments were also conducted on the equilibrium distribution of trans-aconitic acid between its aqueous solutions and a mixed solvent: tributyl phosphate (TBP) + hexane (H) (with a volume ratio of 60/40 TBP/H). Analysis of the results shows that the different (H) decreases the selectivity and the distribution coefficient when compared with pure TBP. However, this is not relevant because these properties are still appropriate for extraction purposes. Additionally, a multistage cross-flow extraction process was performed in order to verify the accuracy of the basic equilibrium data and to obtain the number of stages required to extract trans-aconitic acid from its aqueous solutions. This number was also graphically determined by using a distribution diagram in Bancroft's coordinates and analytically calculated assuming virtual immiscibility between the feed and the extraction solvents. The extraction process was also simulated following the procedure contained in the ChemCAD Process Flowsheet Simulator 4.0 and compared with the experimental results.