The solubilities of 6-aminopenicillanic acid and phenoxyacetic acid were determined at 25 degrees C in aqueous solutions of several hydrotropes by the weight disappearance method at different hydrotrope concentrations. Commercially available aqueous hydrotrope solutions employed were 50 mass % sodium butyl monoglycol sulfate, 40 mass % sodium cumenesulfonate, 40 mass % sodium xylenesulfonate, and 40 mass % potassium-sodium xylenesulfonate, all the hydrotrope concentration mass percentages being expressed on a mass/mass basis. At high concentrations, above the threshold hydrotrope concentration, hydrotropes enhance the solubilities of these components differently. The ternary solid-liquid phase equilibrium diagram for the 6-aminopenicillanic acid-phenoxyacetic acid-water system with sodium butyl monoglycol sulfate as a hydrotrope was constructed. Solubilities of 6-aminopenicillanic acid were also determined in the reaction product mixture with or without the 30 mass % sodium butyl monoglycol sulfate hydrotropic medium. A medium of aqueous sodium butyl monoglycol sulfate solution can be used for the better separation of 6-aminipenicillanic acid.