Proline when isolated from gelatin is always contaminated with the closely related amino acid, onuthine, which can not be entirely removed by chemical methods. Chromatographically pure proline can bo obtained through the synthetic route. This paper reports a new method for the synthesis of this amino acid, based on the hydrolytic cyclization of (γ-phthalimidopropyl)-acetamidomalonic ester with hydrobromic acid in the sealed tube. The crude proline thus obtained is purified through its salt with ammonium rhodanilate.