Introduction: Children with a history of bronchopulmonary dysplasia (BPD) may have lower physical activity levels, but evidence to date is based on self-report. This study compared physical activity levels between children born extremely preterm with and without history of BPD, and examined their associations with pulmonary magnetic resonance imaging (MRI) and pulmonary function test (PFT) indices. Methods: This multi-centre cross-sectional study included children aged 7-9 years born extremely preterm, with and without BPD. Children wore a pedometer for one week, then completed the Physical Activity Questionnaire (PAQ), pulmonary MRI, and PFT. Spearman correlations and multivariable linear regression modelling were performed. Results: Of 45 children, 28 had a history of moderate-severe BPD. There were no differences in any physical activity outcomes by BPD status. Higher average daily step count and higher average daily moderate-vigorous physical activity (MVPA) were each correlated with greater forced vital capacity (r=0.41 and 0.58), greater MRI lung proton density at full expiration (r=0.42 and 0.49), and lower lung clearance index (r=-0.50 and -0.41). After adjusting for MRI total proton density and BPD status, a 5% increase in forced expiratory volume at one second was associated with 738 (95%CI: 208, 1268) more steps per day and 0.1 (0.0, 0.2) more hours of MVPA, respectively. Conclusion: School-aged children born extremely preterm have similar physical activity levels to their peers, regardless of history of BPD. MRI and PFT measures suggestive of gas trapping and/or airflow obstruction are associated with lower physical activity levels.