Background and Objectives. Ionizing radiation is widely used in medical imaging for diagnosis and in radiotherapy for the treatment of various medical conditions. However, ionizing radiation can cause damage to healthy cells and tissues, leading to side effects and an increased risk of cancer and other diseases over time. This study aimed to evaluate the possible radioprotective effect of selenium nanoparticles against the damage caused by ionizing radiation. Materials and Methods. This study followed the PRISMA reporting guidelines to present the results. A comprehensive search was performed on electronic databases such as PubMed, Scopus, Web of Sciences, and Science Direct. Initially, 413 articles were retrieved. After removing duplicates and applying specific inclusion and exclusion criteria, 10 articles were finally included in this systematic review. Results. The reviewed studies showed that selenium nanoparticles had anti-inflammatory and antioxidant properties. They effectively protected the kidneys, liver, and testicles from damage. Furthermore, there was evidence of efficient radioprotection for the organs examined without significant side effects. Conclusions. This systematic review emphasizes the potential advantages of using selenium nanoparticles to prevent the negative effects of ionizing radiation. Importantly, these protective effects were achieved without causing noticeable side effects. These findings suggest the potential role of selenium nanoparticles as radioprotective agents, offering possible therapeutic applications to reduce the risks related to ionizing radiation exposure in medical imaging and radiotherapy procedures.