Objective: To investigate the prevalence and severity of menopausal symptoms in patients with breast cancer undergoing adjuvant endocrine therapy and explore the relationships of these symptoms with health-promoting behaviors and social support.Methods: This cross-sectional study investigated 226 participants from December 2020 to December 2021 in China. Data were collected using the sociodemographic information questionnaire, Menopause Rating Scale, the Health-Promoting Lifestyle Profile II, and Perceived Social Support Survey. Multivariate step regression was used to analyze the potential factors of menopausal symptoms.Results: In our sample of 226 patients, 92.9% reported at least one menopausal symptom with a mean score of 13 points (interquartile range, 9-18 points). The highest prevalence of most symptoms included hot flashes/night sweats, fatigue, joint and muscular discomfort, irritability, and sleep problems. In the regression models, health responsibility (β = −0.15, P = 0.03), spiritual growth (β = −0.28, P < 0.01), friend support (β = −0.43, P < 0.01), and other support (β = −0.31, P = 0.01) were negatively associated with menopausal symptoms.Conclusions: The prevalence and severity of menopausal symptoms are high in breast cancer patients undergoing adjuvant endocrine therapy. Higher health-promoting behaviors and social support are associated with fewer menopausal symptoms. The findings highlight the clinical implications in terms of developing appropriate strategies for managing menopausal symptoms.