<p>Although body weight variability has been linked to adverse outcomes, its relationship with mortality in older adults remains unclear. We investigated the association between body weight variability and mortality in older adults using a nationwide cohort from the Korean National Health Insurance Service. Adults aged ≥ 75&#xa0;years who underwent health checkups between 2012 and 2015 were followed until 2022. Body weight variability was assessed using the variability independent of the mean (VIM) based on at least four measurements. Participants were classified by VIM quartiles and weight-change categories. Mortality risks were estimated using multivariable Cox proportional hazards models. Among 616,696 participants, 195,585 deaths occurred during follow-up. Higher VIM was associated with increased all-cause mortality (adjusted HR for highest vs. lowest quartile, 1.62; 95% CI, 1.60–1.64) in a clear dose–response manner (<i>P</i> for trend &lt; 0.001). This association was consistent across subgroups. High VIM was associated with increased mortality regardless of the direction of weight change. Higher VIM was independently associated with an increased risk of all-cause and cause-specific mortality among older adults. Body weight variability itself, rather than the direction of weight change, may serve as a relevant prognostic marker in this population. Further studies are needed to clarify the clinical implications of body weight variability in older adults.</p>