Background: The purpose of this study was to assess the dose distribution and coverage of level Ⅰ-Ⅱ axillary lymph nodes during whole breast tangential field radiotherapy (RT) after breast-conserving surgery in patients with breast cancer. Materials and Methods: The level Ⅰ-Ⅱ axillary lymph node volumes were retrospectively contoured by a single radiation oncologist based on computed tomography simulation data from 44 patients who underwent breast-conserving surgery without axillary dissection and who received postoperative whole breast RT between January and December 2014. The dose distributions of the whole breast tangential RT fields were reassessed in relation to the axillary level Ⅰ and Ⅱ lymph node volumes. Results: : The average doses delivered to level I and I axillary lymph nodes were 49.4% (range, 14.2–94.6) and 30.8% (range, 2.6–71.5) of the prescribed radiation dose, respectively. The volumes receiving at least 95% of the prescribed radiation dose were 12.7% (range, 0–67.4%) for level I and 1.4% (range, 0–7.7%) for level II nodes. Compared to thin patients, the average doses delivered to axillary lymph node levels I and II were significantly higher in overweight patients. Conclusion: The radiation dose coverage of axillary lymph nodes by whole breast tangential RT varies greatly among patients. To safely omit axillary lymph node dissection from the treatment of clinically axillary lymph node negative T1-2 breast cancer patients with 1–2 positive sentinel lymph nodes, standardization and individualization of whole breast RT are necessary.