A magnetic solid-phase extraction (MSPE) method was developed for simultaneous preconcentrations of U(VI) and Th(IV) before their measurements by inductively coupled plasma optical emission spectrometry (ICP-OES). The main idea of this biotechnological application depends on the use of bacteria, thermophilic Bacillus cereus SO-14, as a solid-phase biosorbent. It was immobilized to gamma-Fe2O3 magnetic nanoparticles and used for MSPE. Characterization of the biosorbent was performed using the scanning electron microscope (SEM), the energy dispersive X-ray (EDX) and Fourier transform infrared (FT-IR) spectroscopy. Also, the the best conditions of experimental parameters were examined, and the reliability of the method developed was verified by applying the certified reference materials. Limit of detections (LODs) of the U(VI) and Th(IV) was calculated as 0.008 and 0.013 ng mL(-1) respectively. Relative standard deviations (RSDs) were found to be 1.6 and 2.4 %, respectively, for U(VI) and Th(IV). R-2 was also calculated as 0.9991. Preconcentration factors were achieved as 100 for both elements. It should be highlighted that LODs were critically improved and the sensitivity of ICP-OES was enhanced. (C) 2020 Elsevier B.V. All rights reserved.