Background: The death of a pregnant mother is one of the important indications of evaluating the social and economic improvement of a society and indicates how functional its healthcare system is. Many of the reasons that cause the mother’s death, can be avoided. This study aims to determine the reasons of pregnant mothers’ death.
Materials and Methods: This is a descriptive-analytical study. It retrospectively studies 165 case files reporting the death of pregnant mothers between 2008 and 2013 in Tehran province, using a researcher-made checklist to collect the data needed. 
Findings: According to the findings the reasons documented by the physicians were these: 82 cases (49.6%) unknown, 14 cases (8.5%) respiratory disorders, and 11 cases (6.6%) hypertensive disorder due to pregnancy. According to autopsy reports cardiovascular disorders, 34 cases (20.6%), was the most frequent death reason and respiratory disorders, 24 cases (14.54%), is second in line and gynecologic disorders that includes postpartum hemorrhage and infection is the third in line with the record of 22 cases (13.3%). 
Conclusion: Cardiovascular disorders and respiratory disorders are the two important reasons for pregnant mothers’ death. This marks the importance of the need to prevent these problems, more than ever. During the pre-pregnancy care of mothers who have planned for pregnancy, cardiovascular and respiratory disorders should be checked thoroughly and precisely. Other risk factors such as overweight, non-healthy diet and inadequate physical activities should be identified and the necessary interventions should be done.