Abstract Background Radiotherapy (RT) is one of the most mainstream cancer therapeutic modalities. However, due to the lack of specificity of the radiation adopted, both normal and cancerous cells are destroyed indiscriminately. This highlights the crucial need to improve radiosensitization. This study aims to address this issue by constructing a multifunctional nanospheres that can sensitize multiple aspects of radiotherapy. Results Nanospheres containing high atomic element Bi can effectively absorb ionizing radiation and can be used as radiosensitizers. Cell viability after Bi2S3 + X-ray treatment was half that of X-ray treatment alone. On the other hand, exposed 3-bromopyruvate (3BP) could reduce the overactive oxygen (O2) metabolism of tumor cells and alleviate tumor hypoxia, thereby promoting radiation-induced DNA damage. The combination index (CI) of 3BP and Bi2S3-based RT in Bi2S3-3BP + X-ray was determined to be 0.46 with the fraction affected (fa) was 0.5 via Chou-Talalay’s isobolographic method, which indicated synergistic effect of 3BP and Bi2S3-based RT after integration into Bi2S3-3BP + X-ray. Under the combined effect of 3BP and RT, autophagy was over-activated through starvation-induced and redox homeostasis dysregulation pathways, which in turn exhibited pro-death effects. In addition, the prepared nanospheres possess strong X-ray attenuation and high near-infrared (NIR) optical absorption, thus eliminating the need for additional functional components and could serve as bimodal contrast agents for computed tomography/photoacoustic (CT/PA) imaging. Conclusions The rational design of multifunctional nanospheres with the unique properties provided a novel strategy to achieving high therapeutic efficacy in RT. This was accomplished through simultaneous activation of multiple sensitization pathways by increasing ionizing radiation, reducing tumor oxygen consumption, inducing pro-death autophagy, and providing multiple-imaging guidance/monitoring.