Objective <p>Little is known regarding the association between biological aging and bone mineral density (BMD). This study aimed to assess the effects of biological aging on BMD in US adults.</p> Methods <p>This study included 14,499 adults aged 20 or older from NHANES (2005–2010, 2013–2014, and 2017–2018). Biological aging was assessed using two different approaches: biological age and biological age acceleration. Multiple linear regression was used to investigate the relationship between biological aging and BMD. Generalized additive models and smoothed curve fitting were used to examine the dose-response relationship between biological aging and BMD. Multiple logistic regression was used to investigate the relationship between biological aging and the risk of osteoporosis.</p> Results <p>After adjusting for potential confounders, our analysis revealed a significant inverse relationship between biological age, biological age acceleration, and BMD at various sites, including the femur neck, total femur, trochanter, and intertrochanter. Furthermore, we observed a significant negative linear correlation between biological age, biological age acceleration, and BMD. Additionally, both biological age and biological age acceleration demonstrated negative associations with the risk of osteoporosis.</p> Conclusions <p>Our findings suggest a significant negative association between biological aging and BMD in US adults.</p>