Purpose <p>The aims of this study were to analyze the effects of a 12-week exercise intervention on bioelectrical impedance analysis-derived phase angle (PhA), resistance (R), and reactance (Xc) in breast cancer survivors (BCS) and analyze the relationship between changes in bioelectrical impedance variables and changes in functional capacity and muscular strength.</p> Methods <p>This was a prospective cohort study. Potentially eligible patients were recruited from the Medical Oncology Unit of the hospital. Female BCS older than 18&#xa0;years were offered to participate in the study if they had previously undergone surgery for their primary tumor and there was no evidence of recurrence at the time of recruitment. A 12-week exercise program including resistance and endurance training was performed, including two weekly sessions led by a physical therapist. Measurements were performed at baseline and after 12&#xa0;weeks, including PhA and function-related outcomes. The relationship between changes in PhA and function-related outcomes was assessed using the Pearson <i>r</i> correlation coefficient.</p> Results <p>Sixty-seven BCS women were included in the analysis. A significant increase was found in PhA and functional outcomes after the intervention, as well as a significant decrease in R. Bivariate correlations showed a significant positive correlation between PhA and functional tests (Hand grip, <i>r</i> = 0.37 [<i>p</i> = 0.002], 30-Sit to Stand, <i>r</i> = 0.39 [0.002], respectively).</p> Conclusion <p>A 12-week concurrent exercise program may be effective to improve PhA and R. Additionally, there appears to be a correlation between PhA and Xc with functional capacity outcomes. Finally, baseline PhA, Xc, and R values explained part of the 30-STS and hand grip tests variance at 12&#xa0;weeks, which could suggest its importance in the prognosis.</p>