Radon concentrations in the working sections of the Zonguldak coal mines were determined and activity concentration measurements of natural Ra-226, Th-232 and K-40 radionuclides were performed with high resolution passive gamma-ray spectrometry for coal samples collected from these sections. The Rn-222 concentration was found to be between 15 and 78 Bq m(-3), well below the action limit of 1000 Bq m(-3) according to ICRP65. The annual effective dose to miners due to inhalation of radon was determined to be between 60 and 312 mu Sv. Activity concentrations of Ra-226, Th-232 and K-40 in the coal samples were found to be 13-164, 13-215 and 344-1100 Bq kg(-1), respectively. Radium equivalent activity, dose rate in air and average annual effective dose equivalents were calculated in the range of 66-602 Bq kg(-1), 32-265 nGy h(-1) and 30-244 mu Sv, respectively. The resultant total annual effective doses can be used to minimise the radiological risk to the coal miners.