Background: Many physiological adaptations occur during pregnancy. One such is changes in the respiratory functions and response to exercise. Many studies have been conducted on changes in peak expiratory flow rate (PEFR) in pregnancy, but there are only few studies reporting the effect of exercise on PEFR in pregnant women. Aims and Objectives:To study the effect of exercise on PEFR in pregnant women. Materials and Methods: PEFR was measured in 50 pregnant women in their second trimester of pregnancy in comparison with nonpregnant women (controls). PEFR was measured twice. The first reading was taken at rest and the second after moderate exercise, in the form of walking on a treadmill for 6 min at 12% slope. It was measured using RMS Medspiror. Results: The mean age of the pregnant women was 23.1 ± 2.7 years and that of the controls was 24.3 ± 2.4 years. The mean height was 1.51 ± 0.05 m in pregnant women and 1.51 ± 0.04 m in controls. In pregnant women, PEFR at rest was lower than that in nonpregnant women. The difference was found to be statistically significant. After exercise, the PEFR decreased in both pregnant and nonpregnant women. The percentage of decrease did not change significantly between the two groups. Conclusion: We conclude that although resting PEFR in pregnant women is less, there is not much difference in the response to exercise between the two groups. Thus, pregnant women can be encouraged to exercise regularly.