This study aimed to determine the effects of a school-based multi-component intervention on accelerometer- measured physical activity (PA) and sedentary behavior (SB) in schoolchildren overweight. This is a randomized controlled study with overweight schoolchildren, allocated to experimental group (EG; n = 13; 7.6 ± 0.8 years; 42.9% boys) and control group (CG; n = 17; 8.2 ± 0.9 years; 26.7% boys). The EG was submitted to a 10-week school-based intervention, comprised of PA and psychological sessions (behavioral therapy), and nutritional guidance. The CG followed the daily routine of life. The time of PA and SB were measured using accelerometers used for seven days. To compare mean SB, moderate to vigorous physical activity (MVPA) and total physical activity (TPA), generalized estimation equations (GEE) were used. It was observed that the average time in MVPA and TPA increased significantly in EG at the weekend (+ 40.9 min / day, p < 0.001; and + 51.6 min/day, p = 0.035, respectively) and at full week (+ 62.9 min/day, p < 0.001; and + 225.0 9 min/day, p = 0.038, respectively). There was no significant difference in time spent in SB after the intervention in both groups. Thus, it was concluded that the proposed school-based multicomponent intervention was effective in increasing levels of MVPA and TPA in overweight schoolchildren. This finding can optimize future interventions to promote a healthy lifestyle for schoolchildren in the school environment.