INTRODUCTION Disrupted rest-activity rhythms (RARs) have been linked to poorer cognitive function and Alzheimer's disease (AD) biomarkers. Here we extend this work to midlife women, who commonly experience menopause-related sleep and cognitive problems. METHODS One hundred ninety-four postmenopausal participants underwent a neuropsychological evaluation, 72 h of wrist actigraphy generating RAR variables, and a blood draw to measure AD biomarkers: phosphorylated tau (p-tau181, p-tau231) and amyloid beta (Aβ40, Aβ42). RESULTS Lower interdaily stability (IS) and relative amplitude (RA) and higher interdaily variability (IV) and least active 5 h (L5) were associated with worse processing speed, independent of sleep. Adjustment for sleep significantly attenuated the associations of RA with memory. Lower RA was associated with higher p-tau231 level, independent of sleep. Further adjustment for menopause-related factors modestly accounted for the associations between RAR, cognitive measures, and AD biomarkers. DISCUSSION Weaker RAR, particularly RA, was associated with worse cognitive functions, and higher AD biomarkers levels, possibly linking RAR with AD pathology in women. Highlights Lower rhythm stability and robustness and higher fragmentation were associated with worse processing speed. Lower robustness was associated with higher levels of phosphorylated tau-231. Menopause factors did not attenuate the association between rest-activity rhythms and cognitive function.