Abstract: External radiation therapy and radionuclidebased therapies are widely used in clinical practice, particularly in the treatment of various tumors. After ionizing radiation acts on the body, its direct or indirect effects have different biological effects on the molecules, cells, tissues, and organs of the body. Deep research and understanding of ionizing radiation and its biological effects are important for efficient application of nuclear technology. This paper reviews the use of ionizing radiation in medicine and its radiobiological effects in order to serve as a reference for the wider application of nuclear technology in medicine.