To provide novel crystals useful as an ingredient for the production of a diabetes remedy. The invention is concerned with .alpha.-form crystal and .beta.-form crystal of (R)-2-(2-aminothiazol-4-yl)-4'-[2-[(2-hydroxy-2-phenylethyl)amino]ethyl]a- cetanilide. The .alpha.-form crystal does not exhibit hygroscopicity and has stability such that it can be used as a medicine, and is useful for mass synthesis in the industrial production. The .beta.-form crystal does not relatively exhibit hygroscopicity and is also useful as a production intermediate of the .alpha.-form crystal.