Maternal obesity and excess gestational weight gain (GWG) are associated with increases in infant birth weight and childhood obesity. While greater levels of physical activity are associated with lower GWG and may contribute to reduced infant birthweight and infant adiposity, this remains to be substantiated. PURPOSE: The objective was to examine the relationships between aerobic physical activity during pregnancy, maternal cardiorespiratory fitness, GWG, and infant adiposity from birth to one year of age. METHODS: Nineteen pregnant mothers with singleton pregnancies were randomized into either aerobic intervention (N=9) or control (N=10) groups and followed for 12 months postpartum. At 12±2 weeks, 20±2 weeks and 36± 2weeks, maternal cardiorespiratory fitness (VO2peak ml/kg/min) was assessed using cycle ergometry, percent body fat via skinfolds, and 5-day levels of physical activity with the BodyMedia Sensewear Armband. Infant skinfolds, length, weight, and waist circumference were obtained at birth, 6 months, and 12 months postpartum. RESULTS: Higher total energy expenditure, moderate to vigorous physical activity (MVPA), step count, and MET level were associated with lower maternal percent body fat (range r = -.59 to -.82; p<0.02) and GWG (range r = -.32 to -.40; p≤0.05). Multiple linear regression analysis with energy expenditure, MVPA, step count and MET level included in the model showed that, MVPA independently predicted 43% of the variability in maternal percent body fat and that MET level independently predicted 22% of the variability in GWG. Total time spent in physical activity during pregnancy did not associate with infant adiposity at birth or during follow-up. However, women with higher cardiorespiratory fitness participated in greater MVPA throughout pregnancy compared to those who were less fit (67.1 ± 38.3 vs. 23.8 ± 23.6min, p<0.001). At the 1 year time point, for every 1 unit increase in maternal cardiorespiratory fitness, infant waist circumference, biceps skinfolds and triceps skinfolds decreased by 1.4cm, 1.6mm, and 1.1mm, respectively (p<0.05). CONCLUSION: Our findings suggests that greater cardiorespiratory fitness is associated with reduced infant adiposity up to one year of age, possibly mediated by levels of moderate to vigorous physical activity throughout pregnancy.