Denatured soluble proteins (DSP), or hydrothermal soluble proteins (peptides) were treated at hydrothermal conditions and their characteristics (foaming property, antioxidant activity and hypotensive effect) were evaluated. To enhance the yield of DSP, base additives and microwave heating were found to be effective. The maximum yield of DSP at 190 degrees C by microwave heating in the presence of base additive for 1h was 80% based on the original amount of protein in a defatted soybean. The peak of molecular weight distribution of DSP by GPC was around 10 kDa. The foaming capacity and foaming stability of DSP were higher than that of alkali soluble (60 degrees C, 30 min, pH 8 NaOH solution) soybean protein. Antioxidant activity (AA) was 63% and that of commercially available soluble protein isolated (SPI) was 64%. AA is closely related to the order of amino acid polymerized (such as histidine, proline and hydrophobic amino acid) and thus DSP probably consisted of histidine and proline in its structure. Hypotensive effect of DSP was measured by angiotensin converting enzyme (ACE) inhibition effect and was found to be positive while IC50 of DSP was 0.66 mg/L compared with 3.3 mg/L of SPI and thus DSP is superior to SPI in view of hypertensive effect.