Aims: There is evidence that physical activity plays an essential role in preventing illnesses during pregnancy. This study aimed to determine facilitators, barriers, and structural factors of physical activity in nulliparous pregnant women: A qualitative study using MAXQDA. Participants & Methods: This qualitative study was conducted from January to June 2020 in nulliparous pregnant women. Forty participants selected randomly from the Pounak Health Center of Tehran City, Iran, answered open-ended questions about the obstacles that deprived them of physical activity during pregnancy. Data were analyzed by MAXQDA 12 software. Findings: According to the results, 620 primary codes, 42 secondary codes, 11 sub-themes, and 6 themes were extracted. These themes were divided into the PEN-3 categories,facilitators, barriers, and structural factors. The nurture factors as facilitators had communication and support from others as sub-themes. Barriers consisted of socio-cultural (participate in pregnancy loss with a companion,social beliefs,culture of poverty), socioeconomic (financial problems), individual factors (physical, psycho-emotional, and spiritual dimensions), and structural factors consisting of environmental (equipment) and organizational (possibilities in health centers) factors. Conclusion: It is essential to comprehend why pregnant women face obstacles to physical activity. Many issues are proposed: the need for enough information on the advantages of physical activity and the role of nurturing factors that need to be motivated to physical activity. Therefore, its a need to investigate structural problems in the community to provide facilities for pregnant women to have physical activity during pregnancy.