Sleep is an active process that affects an individual’s daily functioning and physical and mental health. It is also beneficial for an individual’s overall health and well-being. Children with autism often have difficulty sleeping. One common complaint from parents of children with autism is that these children lack sufficient sleep. The purpose of this study was to examine the effects of physical activity on sleep in children with autism. There were three specific research questions for this study. The first question was to examine the amount of physical activity during the day to determine if physical activity had a beneficial effect on sleep. The second question was to examine the effect of physical activity within 1 hour of bedtime on sleep. The third question was to examine the effect of physical activity within 2-3 hours of bedtime on sleep. Twelve children between the ages of 3 and 11 years with autism who have a sleep problem participated in this study. Children’s physical activity and sleep were assessed with an Actiwatch® for 14 consecutive days. During this time, all children maintained their normal daily routine and parents completed a sleep log. The sleep logs were used to determine what time the children went to bed and what time the children woke up. The effect of physical activity on sleep was examined by comparing the 5 most active days vs. the 5 least active days within a child’s 14 days of data collection. A one-way repeated MANOVA showed that there was a significant effect, Wilk’s Lambda =.32, F (3, 9) = 6.51 (p < .05), partial η2 = .68. The follow-up univariate analysis indicated that the amount of physical activity one hour prior to bedtime has a negative effect on sleep efficiency, F (1, 11) = 8.88, (p < .05), partial η2 = .45. This finding is similar to previous reports stating that physical activity prior to bedtime can be disruptive for sleep. There were no other effects of physical activity on sleep in children with autism determined in this study. These results did not provide support for the effect of physical activity on sleep in children with autism. Since this study only tested 12 children with autism, future research should be conducted with a larger sample size. It is also suggested that future research use a physical activity intervention and more consecutive days of data collection. Keyword(s): adapted physical activity, medical/medical care, research