Total locomotor activity was studied in 10 Thoroughbreds housed under a natural 12/12 light/dark cycle. Five horses were housed in individual boxes, and five were housed in individual boxes with a paddock. In order to record locomotor activity, on each horse was placed an Actiwatch-Mini® (Cambridge Neurotechnology Ltd, UK), actigraphy-based data loggers that record a digitally integrated measure of motor activity. Locomotor activity in the different experimental conditions was evaluated by visual inspection. Average amount of activity (bout of activity/hour) during light and dark phase and cosine Peak (time of peak activity) were calculate using Actiwatch Activity Analysis 5.06. Student’s t-test was used to determine significant differences. The results from this study underline the influence of stabling conditions on activity rhythms in horses; furthermore, we clearly established that in horses, the activity rhythm reaches its peak in the middle of the day.