The prevalence of canine obesity continues to increase and is due, in part, to inadequate levels of physical activity (PA). Accelerometers have emerged as a useful tool to objectively quantify levels of physical activity in humans, as well as companion pets, but there is little data on the levels/patterns of free-living physical activity in pet dogs and how it relates to body condition score (BCS) and owner physical activity. PURPOSE: To quantify free-living physical activity levels of healthy pet dogs using a collar-mounted accelerometer and to relate this to BCS and owner-reported dog walking behavior. MATERIALS AND METHODS: We recorded anthropometric data, BCS and five consecutive days of free-living physical activity via accelerometry in 74 dogs. Four consecutive days of one-minute accelerometer count epochs were summed to generate a measure of hourly and total daily physical activity levels. We also recorded step counts in 49 owners who were instructed to wear a hip-mounted pedometer while walking their dog and record the number of steps following each walk. RESULTS: Mean (SE) accelerometer counts/day were 202,859(5,806). Dogs with a BCS of three were significantly more active than those with a BCS of four (p= 0.047). Dogs were more physically active in the morning and evening hours, presumably because their owners were present. Dogs appeared to engage in distinct periods of PA such that 40% or more of total daily activity occurred during three hours or ∼12% of each day. We analyzed 169 days of owner walks. Mean (SE) accelerometer counts recorded during a walk and corresponding pedometer counts were 95,905(5,637) and 4,558(305) respectively. There was a significant positive relationship between accelerometry counts and steps (r² 0.63, p<0.001). DISCUSSION: These data support the use of accelerometry to assess free-living physical activity in dogs and show that physical activity levels of dogs are inversely related to their adiposity. The strong relationship between dog physical activity and owner dog-walking suggests that interventions aimed to increase walking in dogs may benefit both the dogs and their owners. Accelerometers may be useful in a clinical setting to measure the effects of such interventions.