Background: The aim of this study was to explore whether postmenopausal breast cancer survivors undergoing aromatase inhibitor therapy differ from healthy postmenopausal women in their response to the same aerobic + resistance training. Methods: The participants were separated into two groups: postmenopausal breast cancer survivors undergoing aromatase inhibitor therapy for an average of 20 months (18 women) and healthy postmenopausal women (24 women). We assessed aerobic capacity (predicted maximum oxygen uptake (VO2max) and maximum running velocity test (Vmax)) through a walking test, upper and lower body muscle strength using an estimated one-repetition maximum test, and body composition by dual-energy X-ray absorptiometry at baseline and at three, six, and nine months, respectively. The exercise program was performed three times/week over nine months and consisted of 40 min of machine-based strength training (seated cable row, bench press, leg extension, leg press, and leg curl, as well as bridge, abdominal, and standard plank exercises) followed by 30 min of treadmill walking. Analysis of variance (ANOVA) with repeated measures was used to compare the groups over time. Results: Postmenopausal breast cancer survivors undergoing aromatase inhibitor therapy and healthy postmenopausal women presented similar improvements in estimated lower body strength, predicted VO2max and Vmax, and body fat mass. For maximal upper body strength, there was a significant group x time interaction after six months of training (p = 0.01). The healthy postmenopausal women presented a significant increase in upper body strength after six months, while postmenopausal breast cancer survivors undergoing aromatase inhibitor therapy demonstrated an improvement only at nine months of training. The breast cancer survivors undergoing aromatase inhibitor therapy presented increased lean mass while healthy postmenopausal women maintained values over time (Breast cancer: 33.7 ± 3.9(Pre) vs. 34.1 ± 3.4 kg (Post) and healthy women: 36.4 ± 5.1 (Pre) vs. 36.4 ± 5.0 kg (Post), p = 0.004). Conclusion: Our findings suggest that postmenopausal women undergoing aromatase inhibitor therapy for breast cancer demonstrated adaptations and similar trainability to the same regimen of resistance + aerobic training as healthy postmenopausal women. Implications for Rehabilitation Combined exercise program (aerobic plus resistance) is an important non-pharmacological strategies to improve strength, aerobic capacity, and body composition in breast cancer survivors undergoing aromatase inhibitor therapy. Furthermore, it is important to highlight that the time of intervention seems to influence the upper body strength response in this population. This study showed that trainers and other specialists do not need to modify the prescription of exercise related to healthy women, since the combined exercise program induced similar benefits in strength, aerobic capacity, and body composition in postmenopausal breast cancer survivors undergoing aromatase inhibitor therapy and healthy postmenopausal women.