Abstract Background Self-reported time spent standing has been associated with lower risk of mortality. No previous studies have examined this association using device-measured standing. Method This was a prospective cohort study of 5878 older (median age = 80 years), racial/ethnically diverse, community-dwelling women in the WHI Objective Physical Activity and Cardiovascular Health Study (OPACH). Women wore accelerometers for 1 week and were followed for mortality. The study applied previously validated machine learning algorithms to ActiGraph GT3X+ accelerometer data to separately measure time spent standing with and without ambulation. Cox proportional hazards models were used to estimate mortality risk adjusting for potential confounders. Effect modification by age, body mass index, moderate-to-vigorous physical activity, sedentary time, physical functioning, and race/ethnicity was evaluated. Results There were 691 deaths during 26 649 person-years of follow-up through March 31, 2018 (mean follow-up = 4.8 years). In fully adjusted models, all-cause mortality risk was lower among those with more standing without ambulation (quartile [Q] 4 vs Q1 HR = 0.63; 95% CI = 0.49–0.81, p-trend = .003) and more standing with ambulation (Q4 vs Q1 HR = 0.50; 95% CI = 0.35–0.71, p-trend < .001). Associations of standing with ambulation and mortality were stronger among women with above-median sedentary time (HR = 0.51; 95% CI = 0.38–0.68) compared to women with below-median sedentary time (HR = 0.80; 95% CI = 0.59–1.07; p-interaction = .02). Conclusions In this prospective study among older women, higher levels of accelerometer-measured standing were associated with lower risks of all-cause mortality. Standing is an achievable approach to interrupting prolonged sedentary time, and if not contraindicated, is a safe and feasible behavior that appears to benefit health in older ages.