Introduction: Physical activity (PA) plays an important role in health promotion as well as disease prevention, especially among young adults. The aim of this study was to determine the knowledge, attitudes, and practices towards PA among medical sciences students living in university dormitories in Semnan, Iran. Methods: In a cross-sectional study, 421 students living in the dormitories of Semnan University of Medical Sciences, Semnan, Iran, were randomly included to the study. Students' knowledge of physical activity (KPA), attitudes of physical activity (APA), and practices of physical activity (PPA) were investigated using a targeted questioner. The obtained data were analyzed using SPSS 22.0 at the significance level of 0.05. Results:Participants included 165 (39.2%) male and 256 (60.85%) female students with the mean age of 21.05 ± 2.7 years. The mean scores of KPA, APA and PPA were 48.74 ± 16.01, 58.91 ± 9.02, and 232.5 ± 334.42 minutes per week, respectively. Students' APA had a significant correlation with age (P value = 0.007, r = 0.70) and there was a significant difference (P value = 0.008), between recorded APA from the male group (57.40 ± 10.01) compared to the female group (59.88 ± 8.20), whereas no statistically significant correlation was seen between other variables in the study (P > 0.05). Conclusions: Most of the students had moderate KPA and APA and also an unfavorable PPA. More attention should be paid in improving the KPA, APA, and PPA of medical sciences students living in university dormitories.Keywords: Physical Activity, Students, Dormitories, Medical Sciences IntroductionPhysical activity (PA) plays an important role in the prevention of being overweight as well as obesity in adults. Regular exercise, as a health-promoting behavior, can prevent or delay a variety of chronic diseases and premature deaths. Furthermore, regular PA and exercises can have a profoundly positive impact on ones mental health, which are associated with reduced depressive symptoms and anxiety, increased marital satisfaction, and improved quality of life (1-3).Physical inactivity can double the risk of developing cardiovascular diseases, type 2 diabetes, as well as obesity (4, 5). Today, a majority of the urban population experiences physical or mental illnesses and fatigue. Moreover, the level of physical inactivity is also on the rise in developing and developed countries (3, 6). According to the research findings released by World Health Organization, physical inactivity is the fourth leading risk factor for deaths worldwide causing an estimated 2 million deaths annually. According to the statistics reported by this organization, it is estimated that about 1,240,000 deaths and 1,243,000 potential years of life lost are the consequences of physical inactivity in the Eastern Mediterranean regions (4). PA was considered in some studies (7,8).Regular exercises (30 minutes a day and 3 times a week) is a proven way to reduce cholesterol and it also raises highdensity lipoprotein (HDL) and lowers low-density...