The aim of this randomized clinical trial is to compare the efficacy of Intravenous Dexamethasone and N-Acetyl Cysteine nebulizer plus Intravenous Dexamethasone in treatment of infants' Respiratory Distress Syndrome. The Target population is 60 infants. Preterm infants with respiratory distress syndrome admitted in NICU ward of our hospital will be assessed for eligibility.infants with birth weight between 1000-2500 gr,Gestational age of less than 36 weeks, Mechanical ventilation for at least two days and Oxygen saturation of more than 30% after extubation will be included in the study. Patients with Hemorrhagic lesions, Congenital Anomalies, Chromosomal Anomalies, early sepsis and death before 72 hours of age will be excluded from the study.Patients will be randomly allocated to two groups; first group will receive 0.15 mg/kg of IV Dexamethasone (every 12 hours) and second group will receive 400 mg of N-Acetyl Cysteine nebulizer every 8 hours for 3 to 5 days. Main outcome measures including respiratory rates, arterial oxygen saturation, distress and retraction and need for repeated intubation will be evaluated for assessing efficacy of treatment. Oxygen dependency, blood pressure, blood sugar, pneumonia, sepsis, pneumothorax and other adverse effects and complications will be evaluated.