In order to invetigate the natural radioactivity levels of typical building materials in Nanjing, Jiangsu Province,China, the specific activities of natural radionuclides (226Ra, 232Th and 40K) in samples of building materials were measured by ORTEC HPGe gamma ray spectrometer. And the radium equivalent activity, the internal and external exposure index, and relative annual effective dose equivalents were also claculated. The average concentrations of all the samples ranged from 64 to 318.79 Bq·kg-1, 11.35 to 144.83 Bq·kg-1 and 92.57 to 951.68 Bq·kg-1 for 226Ra, 232Th and 40K, respectively. Their average values were in the ranges: 0.33-1.50 for the internal exposure index (Ira); 0.29-1.51 for the external exposure index (Ir); 0.34-1.74 mSv·a-1 for HEext and 0.36-1.76 mSv·a-1for HEint. The average radium equivalent activity varied from 106.49 to 541.77 Bq·kg-1. According to the standard, most samples were in a lower radioactivity level expect a few of artificial tiles. But, we must perfect detection and management system of many materials to ensure radiation safety and physical health.