Weight gain and obesity are a important problems in breast cancer patients. A cross-sectional study was conducted with 147 BCSs. This study demonstrated the influence of obesity on health-related fitness, anthropometric measures, and cardiovascular state. Introduction: More than half of breast cancer survivors (BCSs) are obese at diagnosis and experience approximately 50% to 96% of weight gain during treatment that could physically affect their survival. The aim of the study was to evaluate the influence of body mass index (BMI) on physical, anthropometric, and physiological parameters in BCSs. Patients and Methods: A cross-sectional study was conducted with 147 BCSs. Health-related fitness, anthropometric measures, cardiovascular state, and cancer-related fatigue (CRF) were assessed for our analysis and 3 groups were formed. Results: Tests of force handgrip (affected side: F = 3.44; P < .05; nonaffected side: F = 3.067; P < .05), functional capacity (F = 3.239; P = .043), and endurance of trunk flexors (x2 = 8.264; P = .016) were significantly lower in obese BCSs compared with the normal-weight group, whereas systolic (F = 5.839; P = .004) and diastolic blood pressure (F = 8.794; P < .001), waist circumference (F = 85.81; P < .001), and arm circumference at 10 cm (affected side: F = 23.530; P < .001; nonaffected side: F = 17.095; P < .001) and 5 cm (affected side: F = 21.751; P < .001; nonaffected side: F = 22.490; P < .001) were significantly greater in BCSs with higher BMI compared with other groups. No significant differences were observed between groups regarding lower limb endurance, resting heart rate or CRF. Conclusion: This study demonstrated the influence of obesity on health-related fitness, anthropometric measures, and cardiovascular state.