Objective To explore the effects of hypoxia on the expressions of hypoxia inducible factor-1α（HIF-1α）, hypoxia inducible factor-2α (HIF-2α) and hypoxia inducible factor-β (HIF-β) in human lung cancer cell lines and their correlations. Methods Six lung cancer cell lines (SPCA1，A549，H446，SH77，H520 and 95D) were incubated under 0.5% OSUB>2/SUB> for 4 to 24 hours.Western blotting and real-time RT-PCR were used for protein and mRNA analysis of HIF-1α, HIF-2α and HIF-β. Results Both HIF-1α and HIF-2α mRNAs were at very low levels or almost undectable under normoxia, as well as their proteins. HIF-1α mRNA experienced a decrease after transcient hypoxia, while the level of HIF-2α mRNA increased. By contrast, under chronic hypoxia, the levels of both HIF-1α and HIF-2α mRNA increased steadily. HIF-1α and HIF-2α proteins were accumulated and changed differently under prolonged hypoxia. HIF-1α was expressed in all the cell lines at various levels, but HIF-2α protein was absent in some cell lines. While both the levels of HIF-β mRNA and HIF-β protein w