Defatted soybean flour was subjected to isolation procedures as follows: NaOH extraction / acid precipitation, water extraction / acid precipitation, NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation.           NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation caused precipitation of one protein mainly consisting 11 S (glycinin) and 7 S (β-conglycinin) respectively. In contrast, NaOH extraction / acid precipitation and water extraction / acid precipitation precipitated the two major soybean proteins as judged by PAGE and SDS-PAGE.           Using differential scanning calorimetry (DSC), NaOH extraction / acid precipitation showed two thermal transition peaks at 72.8^oC and 86.4^oC, where as both NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation observed only one endothermic peak at 85.3 ^oC and minor peak at 75.3^oC, which may corresponding to 11S (glycinin) and 7 S (β-conglycinin) respectively. Second recycling of the thermal properties of all soy isolates exhibited irreversible denaturation behavior.