The specific activities of ~(40 )K,~(226 )Ra and ~(232 )Th and radon exhalation rates of building materials in Xining were determined by using low background multi-channel NaI(Tl)γspectrometer and ERS-2-S radon-thoron analyzer,respectively.The results were evaluated in accordance with the relevant standard methods.The results show that the specific activities of ~(40 )K,except for red-clay brick,gravel aggregate and sand,in the building materials are lower than the mean of local soil,while the specific acti...