One of the most fundamental questions in animal ecology concerns the activity patterns of animals and the environmental and intrinsic factors that influence such dynamics. Activity patterns of the elusive and endangered giant panda (Ailuropoda melanoleuca) are not well understood. Using GPS collars equipped with dual-axis accelerometers on captive and wild giant pandas for the first time, we investigated the impact of day, season, and weather on wild panda activity in Wolong Nature Reserve, Sichuan, China. Most pandas were not crepuscular as previously reported but had 3 apparent activity peaks, in the morning, afternoon, and around midnight. We found a peak in panda activity in June, then an apparent decrease in August and September, followed by an increase again from November to March of the following year. Activity patterns roughly corresponded to mean daily movement distances across seasons and movement behavior in a GPS-collared captive panda (studied to establish a baseline for interpreting collar-recorded activity of wild pandas). There was greater activity in times of higher solar radiation throughout every season, especially under cold conditions. This result suggests the potential for climate change to impact panda behavior in ways not previously reported. Our analysis also suggests that pandas may be constrained by tight energy budgets from their low-nutrient diet and may adjust their energy budgets by modifying their activity time and level across seasons. Our study has implications for understanding animal activity patterns across species, particularly relationships among forage, weather, and energy expenditure over time.