Background: Music can influence human behavior and may be used as a complementary therapy in health care. Objectives: To assess the effect of music interventions on symptoms, adverse events, and quality of life (QoL) of breast cancer patients undergoing chemotherapy (CT). Design: Nonblinded, randomized clinical trial. Women with breast cancer undergoing adjuvant CT were randomized into 2 groups—Group Music (GM) or Group Control (GC)—and followed during the first 3 cycles of treatment. Measurements: Sociodemographic data, WHOQOL-BREF, BDI-II, BAI, and Chemotherapy Toxicity Scale were assessed. Patients were evaluated after each session of the first 3 CT cycles. GM underwent a 30-minute musical intervention before CT. There was no intervention in the GC. Continuous data were analyzed by Student’s t test, and χ2 test was used to compare qualitative variables. Results: Higher QoL scores on functional scales were observed for the GM in comparison to the GC after the first and third sessions of CT. Depression ( P < .001) and anxiety scores ( P < .001) and vomiting ( P < .01) incidence were lower for the GM in the third session of CT. All the participants in the GM 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 the music intervention, suggesting a positive effect of the music intervention on adverse events of cancer CT.