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Soy protein has great potential to partially replace petroleum based adhesives. The weakness of protein-based adhesive has relatively low water resistance. Various chemical and enzymatic methods have been employed to improve the adhesive properties of soy protein. This research studied the effects of esterification on adhesive strength, thermal properties, solubility and conformational change of soy protein. Free carboxyl groups of soy protein were esterified with ethanol and different levels of hydrochloric acid as catalyst. Esterification rendered protein molecules more hydrophobicity by grafting the ester groups. With moderate esterification, soy protein showed maximum adhesiveness and water resistance. Hydrochloric acid might have unfolded and denatured protein by hydrolyzation. More ester groups were attached on the unfolded structure of protein. The optimum esterification condition was ten hour and with no catalyst. The hydrolysis and excess hydrophobic groups attaching might be detrimental to adhesive performance especially water resistance.