Purpose: Weight change during adjuvant treatment for early breast cancer is associated with poor prognosis. The long-term evolution of body composition during adjuvant treatment for breast cancer, particularly endocrine therapy, is not well known and new data on this topic is required. The present study assesses the evolution of weight and body composition among 33 postmenopausal breast cancer patients currently treated with endocrine therapy after standard adjuvant chemotherapy including Taxanes. Patients and Methods: Dual-Energy X-ray Absorptiometry (DXA) was used to measure fat and lean body mass. Body water was assessed by multifrequency bioelectrical impedance analysis. The HAD questionnaire and the short version of the IPAQ were also administered. Results: During endocrine therapy, 15.2% (n=5) of the population lost weight and 36.4% (n=12) gained weight. The overall average gain was 2.0kg ±5.5 (p= 0.04). During this period, fat mass, lean body mass and body water increased. Factors linked to fat mass gain are excess fat mass (≥36%) before treatment and weight loss during chemotherapy. In the overall period of adjuvant cancer treatment, 30% of the population gained more than 5% of their initial weight. The average gain was the same as during the endocrine therapy period (2.0kg ±5.4; p=0.031) and was characterized by an increase in total lean body mass, mainly localized in the trunk region. Conclusion: Endocrine therapy appears as a pivotal period in weight and body composition management. Overfat/obese patients and those who lose weight during chemotherapy are more subject to weight and fat mass gain during endocrine therapy.