ABSTRACTIntroductionModerate to vigorous physical activity (MVPA) after breast cancer diagnosis is associated with improved survivorship. However, differences in MVPA by race among breast cancer survivors are not well described in population‐based studies.MethodsWe analyzed data from Carolina Breast Cancer Study Phase 3 (n = 2994, 50% Black) participants to evaluate the trajectory of MVPA from pre‐diagnosis to 18‐month post‐diagnosis. Participants self‐reported MVPA at baseline (pre‐diagnosis) and 6‐ and 18‐month post‐diagnosis and were classified as having any MVPA (> 0 min/week) or no MVPA. Associations between MVPA and demographic, social, and clinical variables were estimated using multivariable logistic regression.ResultsAt baseline, 84.0% of participants reported any MVPA pre‐diagnosis, which dropped to 55.4% at 6‐month post‐diagnosis, then rebounded to 85.1% by 18‐month post‐diagnosis. Among those who had no MVPA pre‐diagnosis, 32.5% and 71.0% became active at 6‐ and 18‐month post‐diagnosis, respectively. Higher income [adjusted odds ratio (aOR) = 1.33, 95% confidence interval (CI) (1.02, 1.74) > $30K vs. < 15K], lower body mass index [aOR = 1.30, 95% CI (1.00, 1.73) < 25 vs. > 30], low area deprivation [aOR = 1.35, 95% CI (1.08, 1.67) vs. high], high area assets [aOR = 1.54, 95% CI (1.23, 1.93) vs. low], and stage I breast cancer [aOR = 1.72, 95% CI (1.22, 2.43) vs. 3 or 4] were associated with any MVPA at 18‐month post‐diagnosis.ConclusionWe identified several demographic and social correlates of any MVPA at 18‐month post‐diagnosis, and together with established clinical correlates (such as late disease), these factors may contribute to breast cancer disparities.