Abstract: Polyphenols were extracted from the leaves of Juglans mandshurica Maxim using an ultrasound-assisted process. Polyphenol content was determined by UV spectrophotometry. The extraction was optimized by a response surface experiment to arrive at the conditions including 70% by volume of ethanol as solvent, a solvent:solid ratio of 15:1, and an ultrasonic treatment of 30 min at 60℃. The polyphenol extract showed an excellent capacity in scavenging free radicals and ions in the order of DPPH radical > superoxide anion > hydroxyl radical > nitrite ion. It was more powerful than what the chemical preservative, such as benzoic acid, can provide. Thus, the polyphenols extracted from leaves of J. mandshurica by the current method could be a new natural antioxidant for potential applications.