PROBLEM TO BE SOLVED: To provide a crystal that is excellent in solubility of a phenylalanine derivative having α4-integrin-inhibitory action in vivo and used for treating, for instance, inflammatory intestinal diseases.SOLUTION: Provided is a crystal of a pharmaceutically acceptable acid salt of a phenylalanine compound represented by formula (I).【課題】生体内でα4インテグリン阻害作用を有し、炎症性腸疾患等の治療に用いるフェニルアラニン誘導体の溶解性に優れる結晶の提供。【解決手段】式(I)で示すフェニルアラニン化合物の医薬的に許容される酸塩の結晶。【選択図】なし