An antioxidant having high antioxidant activity for beverages and food or drugs is provided. The antioxidant having high antioxidant activity can be obtained by getting a soybean protein hydrolysate in which the content of peptide having 500 or less of molecular weight is 50 wt% or more relative to the total amount of peptide and free amino acid.本發明提供一種抗氧化劑可利用於飲食品或醫藥品,且顯示出高抗氧化活性。藉由得到相對肽及遊離胺基酸的總量,分子量小於500的肽的含量為50 wt%以上的大豆蛋白質水解物,能夠得到高抗氧化活性的抗氧化劑。