Objective To detect the changes in protein profile of rats'lung inhaled radon using two- dimensional electrophoresis(2-DE)and MS.Methods Male Wistar rats were exposed to radon with the cumulative dose up to 100,200 and 400 working level months(WLM).The total proteins of rats'lung were extracted and isolated by 2-DE.The different protein expressions were analyzed with ImageMaster 2D Platinum software and obviously altered proteins were digested by trypsin and identified by MALDI-TOF-MS.Resuits Comparison of the 2-DE images between the control and radon-exposed groups indicated 14 up-regulated and 9 down-regulated protein spots,15 of which were identified by MALDI-TOF or MALDI-TOF/TOF MS.Conclusions The 2-DE image of radon groups'lung has changed,and the lung damage effect of radon is related to some proteins.