Objective:To investigate the effect of exercise during pregnancy on the intensity of low back pain and kinematics of spine. Method: A prospective randomized study was deigned. 107 women participated in an exercise program three times a week during second half of pregnancy for 12 weeks and 105 as control group. All filled a questionnaire between 17- 22 weeks of gestation and 12 weeks later for assessment of their back pain intensity. Lordosis and flexibility of spine were measured by Flexible ruler and Side bending test, respectively, at the same times. Weight gain during pregnancy, Pregnancy length and neonatal weight were recorded. Result: Low back pain intensity was increased in the control group. The exercise group showed significant reduction in the intensity of low back pain after exercise (p < 0.0001). Flexibility of spine decreased more in the exercise group (p < 0.0001). Weight gain during pregnancy, pregnancy length and neonatal weight were not different between the two groups. Conclusion: Exercise during second half of the pregnancy significantly reduced the intensity of low back pain, had no detectable effect on Lordosis and had significant effect on flexibility of spine. Objective: To investigate the effect of exercise during pregnancy on the intensity of low back pain and kinematics of spine. Method: A prospective randomized study was deigned. 107 women participated in an exercise program three times a week during second half of pregnancy for 12 weeks and 105 as control group. All filled a questionnaire between 17- 22 weeks of gestation and 12 weeks later for assessment of their back pain intensity. Lordosis and flexibility of spine were measured by Flexible ruler and Side bending test, respectively, at the same times Weight gain during pregnancy, Pregnancy length and neonatal weight were recorded. Result: Low back pain intensity was increased in the control group. The exercise group showed significant reduction in the intensity of low back pain after exercise (p <0.0001). Flexibility of spine decreased more in the exercise group (p <0.0001). Weight gain during pregnancy, pregnancy length and neonatal weight were not different between the two groups . Conclusion: Exercise during second half of the pregnancy significantly reduced the intensity of low back pain, had no detectable effect on Lordosis and had significant effect on flexibility of spine.