Human bronchia epithelia with mtDNA decrease (ρ- HBE) cells generated by treatment of ethidium bromide (EB) were exposed to radon gas in a special inhalation chamber. Cell proliferation was determined by cell survival assay. Cell apoptosis and membrane potential of mitochondria were analyzed by flow cytometry. The results showed that the survival fraction of ρ? HBE cells significantly increased compared with that of ρ+ HBE cells after irradiation with radon and its progeny. Although the apoptosis rate of ρ- HBE cells was lower than that of the ρ+ HBE cells at early period, the total apoptosis rate was increased, along with the membrane potential decrease of mitochondria in ρ? HBE cells. The results indicate that the increased potential of ρ? HBE proliferation correlates with the total apoptotic rate and mitochondrial membrane potential.Cited