Insomnia is a prevalent complaint among pregnant woman especially during last trimester of pregnancy with significant morbidity but, it often remains neglected. Aim: The present study aimed to investigate the effect of practicing walking with deep breathing exercises on insomnia severity among women in third trimester of pregnancy. Research design: A quasi experimental research design was utilized to conduct the present study in Antenatal Clinics at Obstetrics and Gynecology Center in Mansura city. Sampling: A purposive sampling technique was used to select sixty healthy pregnant women complaining from insomnia, at a gestational age from 28 to 32 weeks, have a single tone pregnancy and perform regular antenatal visits. Data Collection Tools: Two tools were used for data collection; the first tool was a Structured Interview Schedule designed by the researchers, it consisted of two parts to record personal data and reproductive history; the second tool was Insomnia Sleep Index (ISI) it composes of 7 components, it was adopted to measures the pregnant women's insomnia severity pre and post intervention. Results: The present study revealed that, the total score of insomnia decreased for the majority of the women after practicing walking with deep breathing exercises at their third trimester of pregnancy. Conclusion: Practicing walking with deep breathing exercises has a positive effect on severity of insomnia during the last trimester of pregnancy. Recommendation: Raising awareness of the pregnant women about the importance of practicing walking with deep breathing exercises to decrease insomnia severity during last trimester of pregnancy.