The aim of this study is to evaluate radiological safety aspects of the utilization of fly ash in concrete manufacturing in the construction industry. The specific activities of (226)Ra, (232)Th and (40)K in one hundred 55 concrete mixture samples incorporating 10, 20 and 30 wt.% of fly ash collected from the 11 coal-fired thermal power plants were measured by means of gamma-ray spectrometry with HPGe detector. The results of the measurement were used to evaluate the radiological safety aspects of utilization of the fly ash as cement replacement in concrete by assessing the radium equivalent activity, the gamma index, the absorbed gamma dose rate and the corresponding annual effective dose due to the external exposure in indoor. The results of evaluation show that all concrete mixture samples are within the recommended safety limits except for concrete mixture samples incorporating 30 wt.% fly ash of Kangal coal-fired thermal power plant. (C) 2010 Elsevier Ltd. All rights reserved.