Indoor 222Rn in high-rise buildings originates inside the building materials, then diffuses gradually through the intergranular spaces of the material into the room atmosphere. Therefore, the radionuclide contents and the physical properties of the building materials are important for indoor 222Rn levels in Hong Kong. In this paper, the radionuclide contents of typical building materials used locally were determined by gamma spectrometry, and the results indicate that the average 226Ra, 232Th, and 40K contents in Hong Kong concrete are the highest known in the world. Physical properties, such as the emanation coefficients and 222Rn diffusion coefficients, were measured in these materials and they are not much different from those in other countries. The effect of surface coatings on 222Rn exhalation rate was studied and the observed reduction was from 2-68%. The 222Rn exhalation rate was found to increase steadily with temperature up to 50 degrees C; at 50 degrees C, the 222Rn exhalation rate can be as high as four times the rate at 20 degrees C.