The extraction of polyphenols from the branches of Magnolia kwangsiensis figlar & noot. (M. kwangsiensis) was studied by ultrasonic-assisted extraction. The extraction condition was optimized by response surface methodology. The antioxidant activities of M. kwangsiensis branch polyphenols were evaluated in aspect of total antioxidant activity, DPPH· scavenging activity and ·OH scavenging effect. Results showed the optimum conditions were acetone concentration 67%, liquid-solid ratio 22 (mL/g), extraction time 20 min, and the yield of polyphenols reached 1.45%. The polyphenols from the branches of M. kwangsiensis had certain total antioxidant activity, but had good scavenging effects on DPPH· and ·OH.