Glycine crystallizes in more than three different polymorphic forms, α, β and γ. The form α and form γ have been prepared by recrystallization and quench-cooling method, respectively. The physicochemical properties of α- and γ-forms of glycine were investigated. Techniques used to study the polymorphs include X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), solubility determination at 10–70°C and inverse gas chromatography (IGC). Based on the surface free energy analysis and solubility measurement, the γ-form is more stable than the α-form at ambient temperature. The influence of additive, sodium chloride, in the determination of the polymorphs was studied. The conformational change of the α-form to γ-form is enhanced by sodium chloride through glycine–NaCl interaction. In the NaCl solution, the nucleation and crystal growth of the γ-form crystals are promoted while the crystallization of α-form is prevented.