Natural radioactivity is responsible for most of the total radiation dose received by human population. Geological materials used in building industry usually become contaminated with naturally occurring radioactive materials. They are used as mixtures in building industry (kaolin, zircon, frit, feldspar), or mechanically processed and used for covering floors and walls of the rooms (granite). In this paper activity concentrations of 226Ra, 232Th and 40K in 6 kaolin, 11 zircon, 18 granite, 3 marble, 6 sand, 4 perlite, 4 feldspar, 5 korund and 1 frit samples imported in Serbia were determined by gamma-ray spectrometry. Activity concentration index, dose rate and annual effective dose were calculated for each of the investigated samples. Measurement of an external gamma dose rate by using a commonly available radiation survey meter can give some indication of the need for further investigations. The absorbed dose rate and annual effective doses for workers in the ceramic industry "Keramika Kanjiza Plus" in Serbia working with granite are determined.