Eight patients treated with modified radical mastectomy and fenestration of pectoralis muscle to preserve pectoral, nerves are reported and the practical procedure is introduced. The results indicate that this method can overcome the disadvantage of mastectomy (Auchincloss) in that only dissection of fatty tissue and lymph nodes in the lateral part of axilla is carried out. With fenestration of pectoralis major muscle, not only the pectoral nerves can be perserved but also the fatty tissue and lymph nodes, including of those medial to the pectoralis minor, subclavicular and interpectoral nodes can be dissected. This method almost reached Halsted’s demand and it can be used for stage Ⅰ-Ⅱ, and even stage Ⅲ breast cancer if no infiltration to pectoralis major muscle is found.