Objective To assess the effect of inhaled nitric oxide(iNO)on the balance of oxidant-antioxidant of newborns with meconium aspiration syndrome(MAS).Methods There were 55 newborns with MAS who were enrolled in neonatology department of Hebei Province Children Hospital from Febmary 2005 to April 2007.Of the total,25 newborns(group A)were treated with iNO,and the others(grotlP B)were given with conventional mechanical ventilation,witbout iNO.We also selected 30 healthy newborns of our hospital as control group(group C).Both group A and B were given with general treatment,such as tracheal intubation,irrigation of trachea,mechanical ventilation and antibiotics,et al.Group A was given iNO when their legal guardian consented after they had been in hospital for 1-2 hour.And then,we detected the serum level of SOD,MDA and T-AOC of three groups at 0,24 and 72 hour.Results There were significant differences in SOD,MDA and T-AOC among different time points(P＜0.05).With the NO inhaled,the level of SOD,TAOC in group A increased,but the MDA decreased(P＜0.05).The level of SOD in group B decreased early and increased later,while the change of MDA was opposite to it.The level of T-AOC increased as time passed (P＜0.05).Compared with group B,the ventilation time and oxygen exposure time of group A were shoner [(77.38±13.97)h vs(104.27±10.53)h,(158.70±47.23)h vs(202.15±61.92)h](P＜0.05),whereas mortality and incidence of IVH were not significantly different between the two groups.Conclusion The newborns with MAS have an imbalance between oxidant and antioxidant to some extent.Low-dose of iNO shows antioxidant property.It is benefit for the modulation of oxidant and antioxidant balance,and has an antioxidant protection to the body.