ObjectiveTo investigate the value of ultrasound knife in modified radical mastectomy for remaining pectoral nerve and intercostobrachial nerve. MethodsOne hundred and sixty patients with breast cancer were divided into ultrasound knife group and electroscalpe group and then performed modified radical mastectomy with pectoral nerve and intercostobrachial nerve remainning. the pectoralis major thickness and paresthesia of skin of inner upper arm and axillary fossa were detected on the different time after operation. Results①The age, body mass index, and mean opera-tion time had no significant differences between these two groups (P > 0.05).②On 6 months after operation, the thickness of bilateral pectoralis major was not significantly different in the ultrasound knife group (P > 0.05), which of injuried pectoralis major was significantly thinner than that of uninjuried pectoralis major in the electroscalpe group (P < 0.05).③The rates of paresthesia of skin on postoperative 3 months and 6 months in the ultrasound knife group were signifi-cantly lower than those in the electroscalpe group (P < 0.05). ConclusionCompared with monopolar electro diathermy, the use of ultrasonic harmonic scalpel in modified radical mastectomy could better protect pectoral nerve and intercosto-brachial nerve, and thus decrease nerve parafunctional rate.