Background: We investigated the effectiveness of one education course to lower the severity of anxiety and depression symptoms among breast cancer (BC) patients during radiotherapy (RT). Methods: All 290 one-sided BC patients were evenly randomized into intervention or control arm. "Intervention" patient was additionally provided with one three-hour course on psychological stresses and management skills. Changes of anxiety and depression score and their 3-level severity category ('normal', 'borderline' and 'abnormal' scored 0-7, 8-10 and 11-21, respectively) from HADS questionnaire over RT were evaluated by multivariable linear and ordinal logistic regressions. Results: Response rates were 94 and 100% by "intervention" and "control" arm, respectively. Means of score changes by "intervention" and "control" (n = 145) were + 0.59 (SD = 2.47) and + 0.11 (SD = 2.55) for anxiety and + 0.81 (SD = 2.81) and + 0.45 (SD = 2.77) for depression scores, respectively. 'Abnormal' anxiety and depression patients were 4.1 and 6.9% at baseline and 4.8 and 6.9% at end of RT at 'control' arm; those rates were 6.6 and 7.4%, and 8.8 and 10.3% at 'intervention' arm, respectively. Both changes on anxiety and depression measurements between two arms were all insignificant (p > 0.20). Conclusions: One education course did not reduce the score and severity of anxiety and depression symptoms over RT period.