Background: Exercise can profoundly affect physical fitness and quality of life in breast cancer survivors; however, few studies have focused on minorities. This secondary analysis examines Hispanic ethnicity as a moderator of the effects of a 16-week aerobic and resistance exercise intervention on physical fitness and quality of life in breast cancer survivors. Methods: Eligible breast cancer survivors (n = 100) were randomized to exercise (n = 50) or usual care (n = 50). The exercise intervention consisted of supervised moderate-vigorous aerobic and resistance exercise thrice weekly for 16 weeks. Physical fitness and quality of life were measured at baseline, post-intervention, and 28-week follow-up (exercise only). Linear mixed-models adjusted for baseline value of the outcome, age, disease stage, adjuvant treatment, and recent physical activity were used to evaluate effect modification by ethnicity. Results: The study sample included 57% Hispanic and 43% non-Hispanic breast cancer survivors. Hispanic breast cancer survivors were younger, less fit, and diagnosed with more advanced cancers compared with non-Hispanic breast cancer survivors (p < 0.001). Ethnicity was found to moderate the effects of exercise training on all physical fitness and quality-of-life measures including VO2max (8.4 mL/kg/min; 95% confidence interval (95% CI) 3.2 to 13.4), physical well-being (12.3; 95% CI 4.2 to 18.4), and emotional well-being (11.4; 95% CI 5.9 to 15.5). In all cases, Hispanics experienced larger benefits than non-Hispanics. Conclusions: Hispanic breast cancer survivors have poorer cardiorespiratory fitness, muscle strength, and quality-of-life and therefore may derive larger benefits from exercise than non-Hispanic breast cancer survivors. Clinical exercise interventions may attenuate existing health disparities among minority breast cancer survivors. Implication of Cancer Survivors: Here we report psychosocial and fitness-related disparities among Hispanic breast cancer survivors when compared with their non-Hispanic counterparts. Our exercise intervention highlights the importance of exercise for minority cancer survivors and the need for distinct, culturally tailored exercise intervention approaches to reduce psychosocial and fitness-related disparities among this understudied population of cancer survivors.