International Journal of Preventive Medicine (Int J Prev Med)2008-780215102024112057641 Associate Professor of Pediatrics, Neonatologist. Department of Pediatrics, Division of Neonatology, Child Growth and Development Research Center, Isfahan University of Medical Sciences, Isfahan2 Neonatologist, Department of Pediatrics, Division of Neonatology, Child Growth and Development Research Center, Isfahan University of Medical Sciences, Isfahan3 Professor of Pediatrics, Neonatologist. Department of Pediatrics, Division of Neonatology, Child Growth and Development Research Center, Isfahan University of Medical Sciences, Isfahan,4 Associate Professor of Radiology, Department of Radiology, Isfahan University of Medical Sciences, Isfahan20241120Background: The use of vitamin D in premature infants is one of the important preventive factors for osteopenia of prematurity, but there are conflicting results on the appropriate doses, so this study aimed to compare the doses of 400 and 600 units of vitamin D in the prevention of osteopenia of prematurity in infants with a gestational age  ≤32  weeks. Methods: This clinical trial study was conducted on 108 premature infants divided into two groups of 54 with a gestational age of  ≤32  weeks born between 2020 and 2021 in Shahid Beheshti and Al‑Zahrai hospitals in Isfahan. In the first group, daily vitamin D was 400 units from the 7th day of birth, and in the second group, it was 600 units. At the age of 5 weeks, levels of calcium, phosphorus, alkaline phosphatase (ALP), and vitamin D were evaluated. If the ALP level was above 1000, wrist radiography was requested. Also, the baby was examined for clinical symptoms of rickets at the age of 5 weeks. The data were analyzed by Statistical Package for the Social Sciences (SPSS) software version 26, and a P value <0.05 was considered significant. Results: In this study, there was no significant difference between the levels of ALP in the two groups (P = 0.596), but the level of vitamin D was significantly higher in the 600 units of vitamin D group (P < 0.001). The level of calcium was higher in the 400 units of vitamin D group, but this difference was slightly significant  (P = 0.062). The level of phosphorus in the 600 units of vitamin D group was higher than in the 400 units of vitamin D group, and the difference was slightly significant  (P = 0.062). Conclusions: This study showed that daily doses of 600 and 400 units of vitamin D in infants with a gestational age of ≤32 weeks had no effect on the incidence of clinical symptoms and radiological findings of rickets at the age of 5 weeks.http://ijpm.mui.ac.ir/index.php/ijpm/article/view/2945http://ijpm.mui.ac.ir/index.php/ijpm/article/download/2945/717718784