Objective To investigate the effects of cell hypoxia on radio-inducible activity of early growth response gene-1 (Egr-1) promoter and its mechanisms. Methods The reporter vector of Egr-1 promoter was constructed by inserting the promoter sequence upstream the lucifearase gene in pGL3, which was then transfected into the lung adenocarcinoma A549 cell by liposome. The luciferase activity and H 2O 2 production were detected in the transfected cells exposed to doses of 2, 4, 6, 8, and 10 Gy radiation combined with the oxygen concentrations of 0.1%, 0.5%, 1%, 2.5%, and 5 %. The changes of luciferase activity in the transfected cells exposed to various concentrations of H 2O 2 were observed. Results The reporter vector of Egr-1 promoter was constructed successfully. The radio-inducible activity of Egr-1 promoter decreased significantly in the transfected cells exposed to oxygen concentration below 2.5% in a concentration-dependent manner, as compared with that in the normal control (P