Objective: Developing a instruction manual and evaluating results of using radioactive m99TC to identify sentinel lymph nodes in the surgical treatment of early stage breast cancer (I, lIa). Methods: Designing clinical research was used. The study sample consists of 116 patients with stages I and lIa breast cancer who were surgically treated by using radioactive m99TC to identify sentinel nodes in Hanoi Oncology Hospital from 2008 to 2014. According to the TNM Classification of Malignant Tumors (TNM) of Union for International Cancer Control 2002 (UICC 2002), the pathology is adenocarcinoma. Results: The proportion of detecting sentinel lymph nodes by using radioactive is 98.3 percent, the proportion by intraoperative frozen section examinations: inflamed lymph nodes are 71.6 percent, lymph nodes metastasis is 31 percent. The proportion of the sentinel lymph nodes inspection by HE inflamed lymph nodes is 69.8 percent, lymph nodes metastasis is 31.9 percent. The degree of fit between intraoperative frozen section examinations and H.E: 98.7 percent inflamed lymph nodes, lymph node metastasis 94.1 percent with Kappa = 0.87, p0.001, consistent with the very high. Conclusions: As a method of detecting rates of sentinel lymph nodes high, objectively applied well in the specialty cancer hospitals to minimize the complications caused lymph node dissection for patients without lymph node metastasis.