Background <p>Intrinsic capacity is a crucial indicator of adverse outcomes and has predictive value for diseases and mortality. The objective of this study is to assess the association between nighttime sleep duration and intrinsic capacity in older Chinese adults.</p> Methods <p>Data were collected from the China Health and Retirement Longitudinal Study (CHARLS) spanning the years 2008–2020. Minimally sufficient adjustment was made for confounding factors identified through a Directed Acyclic Graphs (DAGs), and multivariate logistic regression analysis was conducted to determine the relationship between nighttime sleep duration and intrinsic capacity. Restricted cubic splines (RCS) were used to assess the nonlinear relationship between nighttime sleep duration and intrinsic capacity in this population. Finally, subgroup analysis and interaction effect analysis were performed.</p> Results <p>Among the 4994 older adults, 3118 (62.4%) experienced a decline in intrinsic capacity. After adjusting for confounding factors, nighttime sleep duration was associated with an increased risk of intrinsic capacity decline (<i>P</i> &lt; 0.001), exhibiting a nonlinear J-shaped pattern.</p> Conclusions <p>For Chinese older adults, increased nighttime sleep duration shows a nonlinear, J-shaped dose-response relationship with the risk of intrinsic capacity decline. Our study provides important insights into the intrinsic capacity and health self-management of older adults.</p>