Background: Though long-term outcomes for pediatric cancer continue to improve, survivors frequently develop treatment-related chronic health conditions. Physical activity may improve quality of life (QOL) and decrease chronic health conditions. Wearable activity trackers are a promising interactive intervention for improving physical activity. Procedure: Participants aged 7-21 years undergoing chemotherapy were invited to participate in a 6-week, single-arm trial. The study had 3 phases: blinded to the watch’s interface, unblinded to the watch’s interface, and unblinded to the watch’s interface while receiving encouraging text messages and suggestions for physical activity. Number of steps, hours of sleep, and minutes of moderate-vigorous activity were collected. Participants and their caregivers completed pre- and post-intervention PROMIS® surveys to assess fatigue, pain, and QOL. Results: Seventeen participants enrolled in the study and wore the activity trackers 84.9% of the study time. The median number of steps and daily active minutes increased from the blinded phase to the unblinded phases (3160 versus 3760, p=0.8951; 26.2 minutes versus 36.7, p=0.8065). Patient-reported fatigue and pain interference pre- and post-intervention improved (54.5 versus 50.2; 52.2 versus 46.6, respectively) and met the minimally important difference (MID). Additionally, caregivers’ perception of their child’s fatigue and life-satisfaction pre- and post-intervention improved (40.2 versus 43.9; 58.7 versus 55.1, respectively) and met the MID. Conclusion: The use of activity trackers was feasible for participants in our study. The results of this pilot study suggest wearing an activity tracker may increase physical activity for children undergoing chemotherapy and lead to improved QOL.