Issue addressed: There is contradictory research assessing physical activity patterns during pregnancy and postpartum among women who are overweight or obese. The aim of this study was to evaluate physical activity among overweight and obese women over the course of pregnancy and the initial postpartum period. Methods: Three hundred and five overweight or obese pregnant women completed physical-activity questionnaires at three time points during pregnancy and at 4-months postpartum. Results: Physical activity declined between early pregnancy and 28-weeks gestation (P<0.001) and declined further at 36-weeks gestation (P<0.001) before increasing significantly at 4-months postpartum (P<0.001). However, reported activity at 4-months postpartum remained significantly lower than that reported in early pregnancy (P<0.001). There was no significant difference either cross-sectionally or for changes over pregnancy and postpartum for total levels or categories of physical activity for women with different body mass index (BMI) or gestational weight gain (GWG). BMI was the only independent predictor of the change in total physical activity over the study and GWG, with women with higher BMI having larger decline of physical activity (β≤0.114, s.e.≤0.750, P≤0.032) and less GWG (β≤-0.253, s.e.≤0.063, P<0.001). Conclusions: Physical activity declined significantly between early pregnancy and 28-weeks gestation, with a further decline to 36-weeks gestation. At 4-months postpartum, physical activity significantly increased but not to the level of that reported at early pregnancy. So what? The promotion of appropriate physical activity should be implemented early in pregnancy and postpartum to prevent the decline in activity we have observed in overweight and obese women. Future research should also explore the barriers and enablers to women engaging in exercise during pregnancy and the postpartum period.