Objective To investigate the effect of radiation on the mitochondrion in adenocarcinoma A549 cells.Methods After A549 cells were irradiated with 0,0.5,3 or 8 Gy of 60Co γrays,mitochondrion membrane potential of A549 cells was detected by JC-1 probe,and ATP activity was measured by ATP kit in a chemiluminescence apparatus.The mitochondria DNA copy numbers was detected by real-time PCR assay.Results At 24 h after radiation,the mitochondrion membrane potential of A549 cells in all the irradiated groups changed significantly (F =243.44,P ＜ 0.05),among which 0.5 or 3 Gy of radiation resulted in a significant increase of mitochondrion membrane potential of A549 cells (t =-10.12,-5.59,P ＜ 0.05).However,the mitochondrion membrane potential of A549 cells exposed to 8 Gy of radiation decreased significantly 24 h after radiation (t =15.22,P ＜ 0.05).The mitochondrion membrane potential of A549 cells in all radiation groups returned to the normal level 48 h after radiation (F =10.36,P ＜ 0.05).24 h after radiation,the level of ATP in A549 cells significantly changed respectively(F =97.08,P ＜ 0.05),similar to the mitochondrion membrane potential.The ATP level in 0.5 and 3 Gy groups increased significantly (t =1.66,7.27,P ＜ 0.05),and the level of ATP in 8 Gy group decreased significantly (t =-8.24,P ＜ 0.05).Furthermore,48 h after both 0.5 and 3 Gy of radiation,the ATP content in A549 cells was still higher than that in untreated A549 cells (t =4.60,8.53,P ＜0.05).The mitochondria DNA copy numbers in A549 cells increased significantly in all the radiation groups (F =118.00,P ＜ 0.05).Compared with untreated A549 cells the mitochondria DNA copy numbers in A549 cells increased at 0.5 Gy by 12 times(t =0.02,P ＜0.05),and increased at 3 and 8 Gy by 7 and 10 times,respectively (t =9.68,15.10,P ＜ 0.05).Conclusions High dose of radiation resulted in the decrease of mitochondrion membrane potential of A549 cells,which subsequently affected the production of ATP.However,radiation with moderate and lower dose could lead to the compensatory increase of mitochondrion membrane potential of A549 cells,which promoted the production of ATP.The mitochondria DNA copy numbers compensatory would increase after A549 cells were exposed to radiation within 8 Gy.