Methods for preparing black soybean hull extracts and uses thereof. The methods can comprise: (1) extracting crushed black soybean hull with aqueous solution containing enzyme and filtering the extracted liquid； (2) ultrafiltration of the extract liquid with an ultrafiltration membrane； (3) absorbing the ultrafiltration liquid with an absorption resin or an ion exchange resin, and elution with ethanol to obtain purified extract liquid； (4) concentrating the purified extract liquid under vacuum； (5) spray drying the concentrated liquid. The extract can contain: 10-45% of cyanidin, 10-25% of catechin, and 40-80% of OPC, and with a total polyphenol content as high as 70-100%. The extract can be used for preparing drugs or food containing antioxidants, or used for improving metabolic syndrome or eyesight.
