ABSTRACT Objectives To explore the association between resting state functional connectivity and accelerometer-measured physical activity in pediatric concussion. Methods Fourteen children with concussion (aged 14.54 ± 2.39 years, 8 female) were included in this secondary data-analysis. Participants had neuroimaging at 15.3 ± 6.7 days post-injury and subsequently a mean of 11.1 ± 5.0 days of accelerometer data. Intra-network connectivity of the default mode network (DMN), sensorimotor network (SMN), salience network (SN), and fronto-parietal network (FPN) was computed. Results Per general linear models, only intra-network connectivity of the DMN was associated with habitual physical activity levels. More specifically, increased intra-network connectivity of the DMN was significantly associated with higher levels of subsequent accelerometer-measured light physical activity (F (2,11) = 7.053, p = 0.011, R a 2 = 0.562; β = 0.469), moderate physical activity (F (2,11) = 7.053, p = 0.011, R a 2 = 0.562; β = 0.725), and vigorous physical activity (F (2,11) = 10.855, p = 0.002, R a 2 = 0.664; β = 0.79). Intra-network connectivity of the DMN did not significantly predict sedentary time. Likewise, the SMN, SA, and FPN were not significantly associated with either sedentary time or physical activity. Conclusion These findings suggest that there is a positive association between the intra-network connectivity of the DMN and device-measured physical activity in children with concussion. Given that DMN impairment can be commonplace following concussion, this may be associated with lower levels of habitual physical activity, which can preclude children from experiencing the symptom-improving benefits of sub-maximal physical activity. KEY FINDINGS What are the new findings? Intra-network connectivity of the default mode network is associated with subsequent accelerometer-measured light, moderate, and vigorous physical activity within the first-month of pediatric concussion Similar associations with physical activity are not observed when examining the intra-network connectivity of the sensorimotor network, salience network, or fronto-parietal network Improved connectivity within the default mode network may lead to increased participation in light to vigorous physical activity in pediatric concussion How might it impact on clinical practice in the future? Default mode network impairment is commonplace in concussion, and this may limit children from experiencing the symptom-improving benefits of physical activity Adjunctive interventions (e.g., mindfulness) that improve the health of the default mode network should be further studied in pediatric concussion