This paper focuses on the natural radioactivity concentrations of 238U, 232Th, and 40K in the eruptive products of the Gölcük Volcano (SW Turkey) and its environmental radiation risks. Concentrations of these radionuclides (238U, 232Th, and 40K) have been measured on different igneous rocks, using a portable gamma-ray spectrometer at 450 points. Based on the obtained data, distribution maps of these radionuclides and the maps showing the absorbed dose rate in the air and radiogenic heat production (RHP) have been generated. We conclude that tephriphonolite and trachytes in potassic-ultrapotassic character display high radioactivity levels. On the other hand, it is revealed that the absorbed dose rate in the air ranging from 21 nGy/h to 482 nGy/h has been calculated as 8 times more than the world average (55 nGy/h). The results indicate that this region has crucial importance on human health and the environment. Therefore, the area requires special attention in terms of radiological hazards and further research should be done in the area regarding this issue. •Radionuclide concentrations definition using the gamma-ray spectrometer in Gölcük volcano.•The comparison of radionuclide concentrations with geology.•The absorbed dose rate in the air has been calculated as 8 times more than the world average.•Radiological hazards on human health and the environment have been determined.