The present invention is to provide a method for obtaining more efficiently isolated-soy protein, which has excellent gelation properties and shows neither bitterness nor astringency characteristic to soybean, while reducing the amount of water used in a soy protein manufacturing plant and thus lessening burden on the environment owing to the reduction in discharged water. It is a method for producing isolated-soy protein, including: an acid-washing step of washing defatted soybeans with an aqueous medium in a region of pH 3.0 to 5.0 to extract and remove whey components; an extraction step of extracting protein from acid-washed soybean slurry obtained in the acid-washing step with an aqueous medium in a neutral to alkaline region and then removing an extraction residue; and an isolation step of separating the extract solution obtained in the extraction step into water and protein while holding it in the neutral to alkaline region.