Abstract: BACKGROUND: Asymmetric Dimethyl Arginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS) is important in different diseases characterized by decreased nitric oxide (NO) availability. We aimed to assess the serum ADMA level in preterm infants suffering from respiratory distress syndrome (RDS) and its relationship with pulmonary outcomes. METHODS: This prospective study included 50 preterm neonates suffering from RDS aging≤32 weeks and weighing≤1500 gm. Serum ADMA levels were estimated in the 1st and 28th day of life by ELISA, and its correlation with surfactant requirement, duration of ventilation, and development of BPD was assessed. RESULTS: Fifty preterm infants with RDS were included, 30 infants were treated with surfactant within 12 hours after birth, the 1stday ADMA level was higher significantly in infants who required surfactant treatment than infants without surfactant treatment, At 36 weeks postmenstrual age, 16 infants were diagnosed with BPD, the 28th day ADMA level was significantly higher in infants with BPD than others without BPD. 1st-day ADMA level was significantly correlated with days on mechanical ventilation but there were no significant correlations between 1st day ADMA and days on CPAP and days on supplemental O2. CONCLUSION: Elevated serum ADMA level in preterm neonates with RDS estimated in the 1st and 28th day of life is a good predictor for pulmonary morbidities such as surfactant requirement, duration of mechanical ventilation, and development of BPD.