Objective:To investigate effects of different state of oxidative stress on fetal rats alveolar type Ⅱ epithelial cells(AECⅡ)cultured in vitro.Methods:AECⅡwere primarily cultured;then randomly divided into three groups of oxidative damage with the oxygen concentration 0.95(95% O2)

0.4(40% O2)and room air(21% O2).Each group was exposed for 12

24 h and 48 h respectively.Then cell morphological change was observed by inverted microscope;and cell survival rate was determined by MTT assay

apoptosis rate and intracellular reactiveosygenspecies(ROS)concentration were determined by flow cytometry.Results:Compared to room air group

survival rate and apoptosis rate of oxygen concentration 0.4 group were not significantly diferent after 12 h and 24 h exposure

but the differences were significant after 48 h exposure

and ROS was significantly different after 24 h exposure;there were significant differences between oxyren concentration 0.95 group and roon air group at three time points.In addition

the morphological change of cells in oxygen concentration 0.4 group was less damage than those in oxygen concentration 0.95 group

but still heavier than those in room air group.Conclusion:After stimulation by 40%O2 over 48 h in vitro

corresponding oxidative damage would also appear in AECⅡ.