Background: Music can influence human behavior and may be used as complementary therapy in health care. Objective: To assess the effect of music therapy on symptoms, adverse events and quality of life (QoL) of breast cancer patients undergoing chemotherapy (CT). Methods: Non-blinded, randomized clinical trial. Patients were randomized into two groups: musical group (MG) or control group (CG), and followed during the first 3 cycles of CT. Sociodemographic data, WHOQOL-BREF, BDI-II, BAI and Chemotherapy Toxicity Scale were assessed. Patients were evaluated after each of the first three CT cycles. MG underwent a 30-minute musical intervention prior to CT. There was no intervention in the CG. Results: Higher QoL scores on functional scales were observed for the MG in comparison to the CG after the first and third sessions of chemotherapy. Depression (p < 0.001) and anxiety scores (p < 0.001) and vomiting (p 0.01) incidence were lower for the MG in the third CT session. All participants in the MG reported positive changes in life in the Subjective Impression of the Subject questionnaire, as well as improvement in fatigue and reduced stress levels. Conclusions: Improvements in QoL, anxiety, depression, and incidence of vomiting were associated with music therapy intervention, suggesting a positive effect of music therapy on adverse events of cancer CT. Clinical trial information: RBR-88r347.