Osteoporosis, primarily characterized by low bone mineral density (LBMD), is a major skeletal disorder among postmenopausal women (PMW), yet its global burden remains poorly quantified. Leveraging data from the Global Burden of Disease (GBD) Study 2021, we assessed the LBMD burden in PMW across 204 countries and territories between 1990 and 2021. Metrics included deaths, disability-adjusted life years (DALYs), years of life lost (YLLs), and years lived with disability (YLDs), with temporal trends evaluated via estimated annual percentage change (EAPC). We found that in 2021, LBMD was responsible for 219,552 deaths and 7.76 million DALYs in PMW globally, with age-standardized DALY rates reaching 979.2 per 100,000 population. Compared to premenopausal women, PMW experienced a 15.17-fold higher mortality, a 5.84-fold higher burden in DALYs, and a 6.29-fold higher burden in YLDs. While age-standardized rates (ASR) for deaths and DALYs showed slight declines from 1990 to 2021, the absolute number of LBMD-related deaths more than doubled, increasing from 91,941 in 1990 to 219,552 in 2021, largely driven by global population aging. South Asia experienced the greatest burden, with India reporting the highest DALYs rates. The burden was highest in women aged ≥80 years and increased most rapidly in those aged ≥95. Regions with a high Socio-demographic Index (SDI) exhibited lower mortality rates but disproportionately higher levels of disability, whereas low-SDI regions bore a greater burden of mortality. Projections to 2045 suggest a sustained rise in deaths and disability, despite modest rate reductions. These findings underscore the urgent need for age-tailored, equity-focused interventions to mitigate fracture risk and improve musculoskeletal health among aging female populations worldwide.