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Background & Objective: Respiratory distress syndrome (RDS) is one of the important causes of newborn mortality. The aim of this study is to determine the pregnancy outcome and Corticosteroid effects for prevention prophylaxis in pregnant women with premature labor between 34-37 weeks gestational age. Materials & Methods: This semi experimental single blind clinical trial study was performed on hundred 34-37 weeks pregnant women who were referred with labor pain or rupture of membrane. These women divided in 2 almost similar case and control groups. The control group received 5 mg Dexamethasone 6 hours to delivery time (Maximum 4 doses). Data was entered to SPSS and analyzed by Chi-square and T-test. Results: There wasn’t any significant difference between administration of Dexamethasone and incidence of RDS in 34-37 weeks newborn (P=0.6). The frequency of RDS was similar in 2 groups (In all women: 4%) the mean weight of newborns with RDS diagnosis was 2675±263. 76% of women had vaginal delivery. The mean weight of newborn was 2672 gr and mean gestational age was 35.4 weeks. Conclusion: The frequency of RDS in newborn with 34-37 weeks gestational age was 4% and administration of one or more Dexamethasone had no effect on reduction it.