Objective To explore the mechanism for the increase in reactive oxygen species regulated by p47phox of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit in peripheral blood mononuclear cells (PBMCs) after oxygen therapy in premature infants.Methods According to different volume fractions of oxygen,premature infants less than 32 weeks were divided into 3 groups:fractional concentration of inspired oxygen (FiO2) ＜ 30％ was low concentration oxygen group,FiO2 between 30％ and 40％ as middle concentration oxygen group,and FiO2 ＞ 40％ as high concentration oxygen group.Premature infants less than 32 weeks without oxygen was control group.After 48 h,3 mL blood was collected via radial artery from each group,PBMCs and serum were separated.Then intracellular reactive oxygen species (ROS) by confocal laser scanning microscopy,malondialdehyde (MDA) within serum by thiobarbituric acid colorimetric,and the location and activation rate of p47phox through immunofluorescence.Results After premature infants were exposed to oxygen,as the oxygen volume fraction was increasing,ROS and MDA gradually rised.More PBMCs with p47phox translocated to membrane,then the translocation rate of p47phox also increased.Compared with the control group,ROS were significantly higher(q =4.48,6.5,16.22,all P ＜ 0.05) among the other 3 groups ; MDA significantly increased as well(q =5.08,8.22,12.76,all P ＜ 0.05) ; the activation rate of p47phox also had significant differences (x2 =134.008,P ＜ 0.05);compared with the middle concentration oxygen group,the high concentration oxygen group had higher ROS and MDA(q =15.03,4.53,all P ＜ 0.05) ; the activation rate of p47phox increased significantly(x2 =19.26,P ＜ 0.05).Conclusions After oxygen exposure,p47phox translocated to membrane may regulate the NADPH oxidase-derived ROS increase in extremely premature infants.