Abstarct: Introduction: Control of body weight and preventing obesity in pregnancy period is a common concern. So, following a good exercise program in women who face with normal peregnancy will promote their health. The aim of this study was to determine the relationship between physical activity and body weight before pregnancy and during pregnancy between pregnant women of Shahrood city. Materials and Methods: In This descxriptive- correlation study that was performed in 1391, 125 pregnant women who has gone to four health-medical centers of Shahrood were studied. For collecting data, the Beck level of physical activity questionnaire and researcher-constructed questionnaires about lifestyle, medicine- exercise and diet record Guide were used .Diet of pregnant mothers was stuied as the registeration of foodstuffs in the past 24 hours and also in a week. Data were analyzed using SPSS statistical software and EXCEL and Kolmogorov - Smirnov statistical tests and Pearson in the level 0/05 ≥ α. Results: The results showed that physical activity level in pre-pregnancy are related with the changes of body weight during pregnancy in pregnant women of Shahrood city (p = 0.006, r = -0.244). Otherwise there is no relation between lifestyle, health status, nutrition and body weight changes during pregnancy in pregnant women of Shahrood city (p ˃ 0.05). Conclusion: Generally and according to this research findings, physical activity before pregnancy has such a considerable influence in weight gain during pregnancy. So, it seems that exercise activities in pre-pregnancy health-care programs can help to maintain the pre-pregnancy BMI in the normal range.