Purpose: The purpose of this study was to analyze the effects of a cognitive-behavioral nursing intervention on anxiety and depression of patients with breast cancer undergoing radiotherapy. Methods: A nonequivalent control group design was used for the study. The research participants were patients with breast cancer (N=71; experimental group=35, comparison group=36) who received radiotherapy at P university hospital. The experimental group received a 6-week cognitivebehavioral nursing intervention (2 hr/week), which included nursing counseling, education about treatment choices for breast cancer and possible side effects and management strategies during radiotherapy, and rehabilitation exercise. Results: Following the intervention, the experimental group showed significantly lower levels of anxiety (Experimental group=$34.60{pm}6.35$, Comparison group=$44.63{pm}9.93$, t=3.552, p<.001) and depression (Experimental group=$10.20{pm}6.61$, Comparison group=$17.81{pm}10.85$, t=3.542, p<.001) than the comparison group. Conclusion: The findings from this study showed that cognitive-behavioral counseling applied by nurses is very effective to reduce anxiety and depression among patients with breast cancer. Therefore, providing nursing counseling to broader spectrum of patients with cancer should be considered. Further research would warrant future clinical application of nursing counseling.