Objective:To explore the feasibility of the tumor-targeted near infrared (NIR) fluorescent dye NIR-T for clearly and accurately delineating incisal edge of breast cancer.Methods:Firstly, the breast cancer xenograft subcutaneous tumor was established in BALB/c nude mice, and dye NIR-T was administrated intratumorally to evaluate the tumor-to-normal tissue (T/N) ratio of the incisal edge of breast tumor. Under the guidance of fluorescence signals, the tumor and peritumoral tissues were resected and collected respectively, and the accuracy of the tumor incisal edge delineated by NIR-T was evaluated by pathological analysis. Studies were further performed on fresh isolated human breast tumor tissues. After intratumoral injection of NIR-T, tumor and peritumoral tissues were collected with the guidance of fluorescence signals, and the accuracy of breast tumor incisal edge delineated by NIR-T was evaluated by pathological analysis.Results:Dye NIR-T was able to clearly delineate the incisal margin of subcutaneous breast tumor in BALB/c nude mice with a T/N ratio of up to 15, and was used to successfully guide the rapid resection of the tumor, and subsequent intraoperative pathological analysis confirmed that the tumor was absolutely removed; NIR-T could be used to clearly delineate the resection margin of breast tumors and its precision was determined to be 100% via pathological analysis.Conclusion:The tumor-targeted NIR fluorescent dye NIR-T was able to clearly and accurately delineate the resection margin of breast tumors, which would promote the precision of tumor resection and shorten the operation time.