Objective: The purpose of this secondary analysis was to test effects of interactions between accelerometer-measured physical activity and self-reported cognitive activity on cognition in older adults without cognitive impairment. Method: Participants were 742 older adults from the Rush Memory and Aging Project who completed annual clinical evaluations. A series of parallel growth models tested effects of interactions between physical activity and cognitive activity on cognition (global index, five domains) at Year 5, controlling for demographics, health factors, and corresponding cognition measures at Year 1. Results: Results were mixed, with significant physical and cognitive activity interactive effects for working and semantic memory. In models without interactions, higher physical and cognitive activities at Year 1 and less decline in cognitive activity over time were independently associated with better cognition at Year 5. Discussion: These findings may inform interventions that enhance physical and cognitive activities to prevent cognitive impairment in older adults.