BACKGROUND: Physical activity is critical for the management of knee osteoarthritis, and the spouse may play a role in encouraging or discouraging physical activity. PURPOSE: The purpose of this study was to examine four types of spousal influence-spouses' daily activity, autonomy support, pressure, and persuasion-on the daily physical activity of adults living with knee osteoarthritis. METHODS: A total of 141 couples reported their daily experiences for 22 days using a handheld computer and wore an accelerometer to measure moderate activity and steps. RESULTS: Spouses' autonomy support for patient physical activity, as well as their own level of activity, was concurrently associated with patients' greater daily moderate activity and steps. In addition, on days when male patients perceived that spouses exerted more pressure to be active, they spent less time in moderate activity. CONCLUSIONS: Couple-oriented interventions for knee osteoarthritis should target physical activity in both partners and spousal strategies for helping patients stay active.