BackgroundParticipation in organized sports is associated with higher physical activity (PA) levels in school-aged-children. Yet, little is known about PA determinants in preschool-aged-children. We examined associations between organized sports participation and preschoolers’ daily PA.MethodsThe study comprised 290 3–5 years old children and PA was measured for 1 week via accelerometers. Organized sports participation was parent-reported and preschool arrival and departure time was teacher-recorded. The preschool duration reported by teachers was matched with time-stamped accelerometer data to distinguish PA during preschool time and PA outside preschool time. Linear mixed models, nested on preschool level, were used to examine associations between organized sports participation and children’s PA outside preschool time, during preschool time and throughout the day.ResultsIn total, 146 children (50.3%) participated in organized sports at least 1 h/week. Participation in organized sports was associated with 6.0 more minutes of moderate-to-vigorous PA (MVPA) (95% CI: 0.6, 11.3) throughout the day and 5.7 more minutes of MVPA (95% CI: 1.6, 9.7) outside preschool time after adjustment. There was no association between organized sports participation and PA during preschool time.ConclusionsThis is the first study to show positive associations between organized sports participation and preschoolers’ PA levels outside preschool time and throughout the day. In addition, findings from this study do not support PA compensation. Therefore, targeting organized sports may be successful in improving PA, even among preschoolers.