Abstract: To explore phase behavior of xanthan gum/lysozyme ( XG/Ly) system induced by in situ acidification and their molecular structural changes during nanogel fabrication, continuous phase transition of XG/Ly system and thermodynamic properties of XG and Ly in the simulated alkali or alkali coupled thermal conditions were analyzed through transmittance and DSC respectively.The results showed that XG/Ly systems transited from co-solubility state to form soluble complexes, and finally produced tenuous network in situ acidification.Interconnection points of pH were 10.46, 10.85 and 10.64 when the ratios of XG/Ly were 3 ∶ 1, 1 ∶ 1 and 1 ∶ 3, indicating that Ly could promote the process of phase transition of XG/Ly system.Thermodynamic analysis revealed that the original structure of XG and Ly changed during nanogel formation.