Heavy fuel oil and ash samples were collected from the Assiut thermal power plant in Egypt and subjected to gamma spectrometry analysis for natural radioactivity contents. Considerable results were observed where the ash contains nearly 1,000 times natural radionuclides more than raw oil. The results were confirmed by measuring the samples via using different devices in different institutions. All ash samples had radium equivalent activities and external hazard index values more than 370 Bq/kg and unity respectively. The mean absorbed dose rate was10,650 nGy/h which is nearly 190 times higher than the global average value of 55 nGy/h. The corresponding annual external effective dose is estimated to be 13 mSv/year, which is nearly 30 times higher than that in areas of natural background radiation (0.46 mSv/year).