Urea induced equilibrium unfolding of fatted and defatted human serum albumin (HSA) showed that fatty acid stabilizes native and intermediate states. Similarly acid induced unfolding of fatted and defatted HSA also showed that fatty acid stabilizes Ntwo left arrowsF and Ftwo left arrowsE transitions. These results also showed that five electrostatic interactions along with one buried carboxyl group of acidic amino acid are involved in acid induced unfolding of HSA.