The ternary phase diagram of L-valine (L-Val)/L-norvaline (L-Nva)/water system was determined at 293.15 K, in which the tie lines clearly indicate the formation of complete solid solution and X-ray powder diffraction (XRPD) analysis of the solid phases further confirms complete miscibility of L-Val and L-Nva molecules in the solid state. Further, homogeneous solid solution can be obtained via mechanochemical method of non-solution system and via anti-solvent method. Similar composition analysis of solid and liquid phase suggests that L-Val and L-alanine (L-Ala) is partially miscible with only a narrow scope of component substitution. The similarity degree of the three amino acids in cell dimensions and supramolecular organization determines the miscibility of L-Val and L-Nva or L-Val and L-Ala, and the investigation in molecular incorporation of L-Val/L-Nva system was developed. Applying the experimental solid-liquid equilibrium data, fractional crystallization is verified as an effective purification method. (C) 2017 Elsevier Ltd.