Background: Neonatal and pediatric health have a great share in global health programs. However, the neonatal mortality rate still shows unacceptable figures and statistics worldwide. Objectives: To investigate the timing and causes of neonatal death. Methods: In this retrospective descriptive study conducted in neonatal care units of Mahdiyeh Hospital in Tehran, Iran, the census sampling method was used to include all the medical records of the expired neonates during 2015-2020. Neonatal and maternal demographics and health complications were recorded. Descriptive statistics such as mean, standard deviation, frequency, and associations were analyzed to compare factors recorded as causes of neonatal death and its timing. A P-value of < 0.05 was considered significant. Results: Out of 24049 live births, 755 neonates had expired (3.1%). The expired neonates' average birth weight was 1616 ± 905 grams, and 35.9% weighed under 1000 grams. Most (80.8%) expired neonates were preterm (30.9 ± 4.8 gestational weeks), and the most common causes of neonatal death were prematurity (23.6%), congenital anomaly (19.9%), respiratory distress syndrome or RDS (19.5%), sepsis (13.2%), and asphyxia (7%). Most (60.7%) neonates died between the second and seventh days of birth. The following conditions were associated with an early-period neonatal death rather than a later-period: multiple births (OR = 2.8), normal vaginal delivery (OR = 2.03), low-birth-weight, diabetic mothers, neonatal heart disease, neonatal neurological diseases, RDS, asphyxia, familial marriage, and intrauterine growth restriction (IUGR) (P < 0.05). Being male (P = 0.005) or being multiple births (P < 0.0001) were associated with a higher risk of death. While 57% of mothers delivered through Cesarean section, among the expired neonates, 66.9% were delivered through Cesarean section. In expired neonates, Apgar scores were low in the first (5.71) and fifth (7.27) minutes of birth. Conclusions: Our study showed that prematurity, congenital anomaly, RDS, sepsis, and asphyxia were the most prevalent causes of death among expired neonates, respectively. Preterm birth and low birth weight were prevalent among expired neonates. Conducting regular similar studies periodically is important to identify, manage, and reduce neonatal mortality rates as an indicator of health promotion in the country.