Solid-liquid equilibria in L-isoleucine (L-Ile) + L-alanine (L-Ala) and water were measured at 293 K using the crystallization method. The L-Ile solubility decreased gradually with increased mole fraction Of L-Ala. However, the L-Ala solubility was not affected by the presence of a small amount of L-Ile. Regarding the solid phase, the formation of a solid solution Of L-Ile and L-Ala was confirmed when solid phases contain much L-Ile. In contrast, only L-Ala crystallized when L-Ala and a small amount Of L-Ile were in the liquid phase.