Background and objective <p>Sarcopenic obesity, defined as the coexistence of reduced muscle mass and excess adiposity, may adversely affect bone health, especially in postmenopausal women with type 2 diabetes mellitus (T2DM). This study aimed to explore the association between different body composition phenotypes, particularly sarcopenic obesity, and bone mineral density (BMD) in this population.</p> Methods <p>We retrospectively analyzed 573 postmenopausal women with T2DM hospitalized between September 2020 and October 2024. Based on appendicular skeletal muscle mass index (ASMI) and body fat percentage (BFP) measured by dual-energy X-ray absorptiometry (DXA), participants were classified into control, obesity alone, sarcopenia alone, and sarcopenic obesity groups. Associations between phenotypes and BMD were assessed using Spearman correlation, logistic regression, and restricted cubic spline (RCS) models.</p> Results <p>The obesity group had the highest BMD, while the sarcopenia group had the lowest. Sarcopenic obesity was associated with significantly lower lumbar spine and hip BMD and a higher risk of osteoporosis. Obesity showed a protective effect (OR = 0.515, <i>P</i> = 0.002), whereas sarcopenic obesity increased osteoporosis risk (OR = 3.368, <i>P</i> = 0.007). RCS analysis revealed nonlinear relationships between ASMI, BFP, and BMD.</p> Conclusion <p>Sarcopenic obesity significantly increases osteoporosis risk in postmenopausal women with T2DM, while isolated obesity may protect bone mass. Routine body composition assessment is essential for early identification and targeted intervention.</p>