Ampicillin is one of the most consumed antibiotics. Due to environmental issues the production of ampicillin has been forbidden by the conventional chemical route. An alternative is the enzymatic route followed by crystallization of the antibiotic. Therefore, this work aims the determination of a series of ampicillin and phenylglycine solubility data in aqueous media using an analytical method. The measurements were carried out at 283.15 and 298.15 K, varying the pH between 3 and 8, and ethanol composition up to 70 wt%. Dissociation constants (pKa's) have also been measured at the studied temperatures and ethanol compositions. It is demonstrated that ideal thermodynamic model with the predetermined pKa's is able to describe satisfactorily solubility profiles. Solubility measurements of ampicillin and phenylglycine have been determined at different conditions of industrial interest. These data may be applied for the evaluation of the crystallization step of ampicillin in the enzymatic synthesis. (C) 2015 Elsevier B.V. All rights reserved.