Effect of L-phenylalanine(L-Phen) on the precipitation behavior and morphology of a L-glutamic acid (L-Glu) crystals, and inclusion of L-Phen in L-Glu crystals were investigated. L-Phen suppresses both nucleation rate and growth rate of L-Glu. morphology of L-Glu was observed to change depending on L-Phen concentration. Two predominant morphologies were obtained, which have the large (111) face and the new face of (110), respectively. Irregular increase of the molar ratio of L-Phen to L-Glu in nucleated crystals was detected and it was attributed to the morphology change of L-Glu crystals. Dependence of R on L-Phen concentration appeared to be different between the nucleated crystals and seed crystals.