This study examined relationships between mother’s physical activity during pregnancy and newborn’s brain cortical development. Healthy pregnant women were recruited and their physical activity level were monitored throughout pregnancy. Their newborns underwent a brain MRI examination at 2 weeks of postnatal age. Brain structural images were post-processed and mean cortical thickness for different brain regions was calculated. We found that at both 1st and 2nd trimester of pregnancy, there were significant positive correlations between mother’s physical activity level and newborn’s brain cortical thickness in multiple regions, suggesting positive impact of mother’s physical activity during pregnancy on offspring brain cortical development.