Normal ageing is associated with increases in cellular and tissue atrophy in the cortices of the brain, which is associated with age-related cognitive decline (1). Age-related cognitive decline is influenced by changes in cortisol secretion caused by dysregulation of the Hypothalamus-Pituitary-Adrenal (HPA) axis (2). Therefore, understanding factors that impact HPA axis regulation may help in determining mechanisms to prevent or delay the progression of cognitive impairment. Physical activity reduces both age-related cognitive decline and cognitive decline associated with neurodegenerative diseases, although the exact biological mechanisms are currently unknown. This study examined the relationship between HPA axis function, measured by morning levels of cortisol, and physical activity in 198 (49% male) healthy older adults (66.95 ± 6.34 years) who volunteered for the Brain in Motion Study. Over 18 months, pre-intervention, intervention, and post intervention measures of morning levels of free blood cortisol were collected and analyzed using ELISA assays. Participants’ lifetime and past year physical activity were assessed pre-intervention with the Lifetime Physical Activity interview-administered questionnaire (3) and were reported in Metabolic Equivalents of Task per year. The 6-month aerobic exercise intervention was a three day a week, supervised program, where intensity of the aerobic exercise was determined individually based on heart rate reserve (4). A series of hierarchical linear regression analyses were conducted to determine the impact of lifetime and past year physical activity on the measures of morning cortisol. Past year physical activity was a significant predictor of morning blood cortisol levels at the 6-month baseline (β = .176, p = .026), with trends noted at the initial baseline (β = .129, p = .098) and at the post intervention (β = .132, p = .088). Past year physical activity did not predict change in morning blood cortisol levels from the pre- to post- exercise intervention (p > 0.05). Furthermore, lifetime physical activity was not found to be a predictor of morning blood cortisol levels taken at any point in the study nor of change in cortisol levels from pre-to post exercise intervention (p > 0.05). These results suggest that past year physical activity is associated with greater HPA axis function, as higher morning levels of cortisol are indicative of a healthier HPA axis (5). These results add to previous evidence that current physical activity is associated with HPA axis health and suggest recent physical activity, not activity levels earlier in an individual’s life, impact HPA axis function in older adulthood.