Abstract Aim: To evaluate the effect of regular aerobic exercise on the endothelial function and cardiorespiratory fitness in pregnant women . Method: This was a randomized, double‐blinded, controlled clinical trial of 64 healthy primigravid women between 16 and 20 weeks' gestation. The experimental group took part in aerobic exercise at an intensity of 50–65% of their maximum heart rate for 60 min, three times a week for 16 weeks. The control group undertook their usual physical activity. The outcomes were the endothelial function evaluated by flow‐mediated dilatation and cardiorespiratory fitness evaluated by the maximum indirect oxygen consumption (VO 2max ) in a 6‐min walk test. Results: Initially, no differences were found between the groups in any of the variables. At the end of the intervention, the participants that performed exercise showed a higher cardiorespiratory fitness, measured by the walked distance in the 6‐min walk test ( P = 0.014) and by the VO 2max ( P = 0.014). Also, the exercise group showed a lower heart rate at rest and a higher flow‐mediated dilatation than the control group ( P = 0.02). Conclusions: Regular aerobic exercise improves endothelium‐dependent vasodilation in pregnancy. This intervention may be an early and effective alternative to strengthen the prevention of disorders associated to endothelial dysfunction.