Provided are a fermentation product, which shows a strong antioxidative effect and is efficacious against diseases caused by active oxygen, and a method of producing the same. Stems and leaves of a perennial gramineous plant (rice straw, reed, barely straw, etc.) are mixed with a fermentation medium which comprises egg albumen, egg yolk, rice bran and water optionally together with xylase and thus the stems and leaves of the perennial gramineous plant are decomposed. After conducting lactic acid fermentation, the contents of the fermentation tank are dried. The dry fermentation product thus obtained is extracted with water and the extract is filtered and then concentrated.