Abstract: Understanding the effect of electrostatic interaction between protein and polysaccharide on the structure and thermal properties of protein could provide new insights into the mechanism of interfacial properties of electrostatic complexes. Herein, the effects of electrostatic interaction between ovalbumin(OVA) and chitosan(CS) on the secondary, tertiary structure and thermal properties of OVA were investigated by UV-vis spectroscopy, intrinsic fluorescence spectroscopy, circular dichroism, Fourier transform spectroscopy and differential scanning calorimetry. The results showed that both electrostatic repulsion and electrostatic attraction could cause the structure of OVA to unfold, which was mainly characterized by the migration of tryptophan residues to the hydrophilic region and the decrease of exposure degree. The contents of α-helix, β-turn and random coil decreased by 26.9%, 52.3% and 6.0%, respectively, and the β-sheet increased by 33.9%. In addition, the thermal denaturation temperature of OVA increased from 78 ℃ to 83 ℃ due to electrostatic binding. These findings could provide a reference for the use of polysaccharides to regulate the functional properties of OVA through electrostatic interaction.