Natural radioactivity of Cayirhan lignite coal treated at Cayirhan (Ankara, Turkey) power plant, its ash and soil samples mixed with ash in the power plant field were investigated. For comparison, soil samples were collected from a distance of 4 kin south of the plant. The analysis shows that the samples include natural radionuclides such as Ra-226, Th-232 and K-40. The mean activity concentrations of Ra-226, Th-232 and K-40 were 57.82, 30.45 and 322.21 Bq . kg(-1), respectively. Obtained values shows that the average radium equivalent activity (Ra-eq), air-absorbed dose rate (D), annual effective dose (AED) and external hazard index (H-ex) for all samples are 123.9 Bq . kg(-1), 58.90 nGy . h(-1), 71.99 mu Sv . y(-1) and 0.34, respectively. The Ra-eq values of samples are lower than the limit of 370 Bq . kg(-1), equivalent to a gamma-dose of 1.5 mSv . y(-1). The measured activity concentrations for these radionuclides were compared with the reported data of other countries. (C) 2007 Elsevier Ltd. All rights reserved.