Objective: Sarcopenia is associated with high morbidity and mortality in older women. Early detection and intervention during the postmenopausal period were hypothesized to help maintain muscle mass and performance. Although the Asian Working Group has developed guidelines for sarcopenia management, the condition has not been sufficiently investigated in the middle-aged cohort of the Asian population. This study aimed to measure the prevalence of pre-sarcopenia and sarcopenia in middle-aged postmenopausal women and to determine the factors associated with low muscle mass. Methods: In this cross-sectional study conducted in the Menopause Clinic, King Chulalongkorn Memorial Hospital, we used the bioelectrical impedance analysis method to determine the appendicular muscle mass using a body composition analyzer (TANITA MC980 Plus). Appendicular muscle mass index, handgrip strength, and 6-m gait speed were measured in 340 women aged 45 to 65 years. Hormonal profiles, anthropometric data, and relevant history were recorded. Results: The mean age of the study participants and time since menopause were 57.8 ± 4.5 years and 9.4 ± 5.5 years, respectively. The proportion of pre-sarcopenic, sarcopenic, and nonsarcopenic women were 11.8%, 2.7%, and 85.6%, respectively. A body mass index ≤ 20 kg/m2 had the strongest correlation with low muscle mass (odds ratio 7.1; 95% confidence interval 3.0-16.8, P < 0.001). Conclusion: Nearly 12% of Thai middle-aged postmenopausal women were pre-sarcopenic. Early detection of symptoms of pre-sarcopenia and maintenance of a healthy body mass index may reduce the burden of this condition for middle-aged and older women.