Abstract: White birch (Betula platyphylla Suk.) bark, one of the important biomaterial resources, is the remains after cutting and processing of the tree. Ultrasound-assisted extraction of betulin from white birch bark using uniform design was optimized. The effects of ultrasound power, extraction temperature, extraction time and liquid-solid ratio on betulin yield was discussed, and betulin content was determined by HPLC. Betulin yield could reach up to 83.43 %±1.89% with the purity of 71.20%±0.74% under the conditions of ultrasound power 400W, extraction time 70min, extraction temperature 70℃, and liquid-solid ratio 40:1(mL:g). Comparing with the traditional reflux extraction, shorter extraction time and better yield were achieved by ultrasound-assisted extraction. Through pre-treatment with 5% sodium carbonate aqueous solution the interference of acidic impurities on the extraction of betulin could be reduced.