Abstract Introduction: Breast cancer patients usually react to mastectomy surgery by increased levels of stress, anxiety and depression which requires effective interventions. The aim of present research was to investigate the effects of an Electromyography (EMG) and heart rate variability (HRV) biofeedback-assisted relaxation training to alleviate the psychological symptoms of mastectomy breast cancer women. Method: In a randomized controlled trial design about 14 mastectomy women were randomly chosen and divided into two groups and measures of Depression Anxiety Stress Scale were gathered for them. The experimental group received biofeedback-assisted relaxation training, whereas no intervention administered on the control group. All subjects again completed the DASS scales afterwards. Indices of smooth artifact free surface Electromyography (sEMG) and HRV biofeedback recorded using a Biofeedback 2000 x-pert system Version 4. Data were analyzed by a General Linear Model: Multivariate Analysis of Variance statistical analysis. Results: Depression, anxiety, and stress average scores showed a significant difference after biofeedback intervention. Significant differences were observed in the sEMG and Heart Rate Variability-Index (HRV-Index) measures of the two groups with better results for the experimental subjects as well. Conclusion: The biofeedback-assisted relaxation training could effectively decrease negative psychological symptoms of the mastectomy breast cancer patients due to sEMG and HRV positive changes and is then recommended for these patients in the course of their treatment.