Abstract： Objective To investigate the effects of hyperoxia on inflammatory response in lung of infantile rats. Methods Forty 21-day-old male Sprague-Dawley (SD) rats were randomly divided into five groups: room-air control group and 12, 24, 48, 72 hours hyperoxia groups, with the rats continuously exposed to room-air and oxygen (92%-94%) respectively. The rats were sacrificed by depletion method, and lung tissue was obtained for bronchoalveolar lavage. The contents of malondialdehyde (MDA) and the activities of myeloperoxidase (MPO) in lung tissue were assayed by thiobarbituric acid or chromometry, and the concentrations of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-10 in bronchoalveolar lavage fluid (BALF) were measured by enzyme linked immunosorbent assay (ELISA). The lung pathology was examined, and lung injury score was assessed. Results Compared with the room-air control group, the contents of MDA [(2.24±0.43) mmol/g vs. (1.57±0.31) mmol/g] and the activities of MPO [(1.24±0.25) U/g vs. (0.69±0.22) U/g] from lung tissue were elevated at 12 hours and 24 hours of hyperoxia exposure, respectively, and they further increased with prolongation of hyperoxia exposure (P<0.05 or P<0.01). The values of TNF-α [(135.2±44.0) ng/L vs. (94.5±22.3) ng/L], IL-6 [(73.1±14.2) ng/L vs. (55.7±17.3) ng/L] and IL-10 [(67.9±21.7) ng/L vs. (48.2±7.6) ng/L] in BALF were all higher at 24 hours of hyperoxia exposure than those of the room-air control group (P<0.05 or P<0.01), but decreased at 48 hours of hyperoxia exposure compared with those of 24-hour hyperoxia exposure group [TNF-α: (105.4±17.0) ng/L, IL-6: (54.3±17.4) ng/L, IL-10: (50.9±6.9) ng/L, all P<0.05]. Lung injury scores were higher at 12 hours of hyperoxia exposure as compared with those of the room-air control group (4.5±1.4 vs. 1.3±0.5), and it further increased with prolongation of hyperoxia exposure (P<0.05 or P<0.01). Conclusion Hyperoxia can lead to lung inflammatory injury in infantile rats, and the expressions of TNF-α, IL-6 and IL-10 in BALF may reach the peak at 24 hours of hyperoxia exposure.