Radioactive waste is an emerging problem in developed and developing countries, especially in the wastewater of nuclear reactors. Radioactive wastewater contains heavy metals and radionuclides, is hazardous in nature, can be a threat to environmental health and thereby needs a sustainable solution. It is crucial to understand the specific characteristics of radioactive waste and treatment processes to ensure the appropriate conditions for effectively controlled remediation. Augmenting levels of radioactive wastewater from industrial and nuclear activities causes detrimental effects on the environment and human health. Traditional methods for treating radioactive wastewater are expensive, energy-intensive, and generate secondary waste. Fungi, however, offer a cost-effective, sustainable and eco-friendly alternative for bioremediation due to their unique abilities. Fungi and other microorganisms play an extensive and fundamental role in the transformation and stabilization of radionuclides in contaminated environments. They can immobilize and remove radionuclides through biosorption, bioaccumulation, biotransformation, bioaugmentation, and precipitation. Fungal hypha provides a large surface area for binding radionuclides, while mycelium networks enhance the immobilization of contaminants. Some fungi are extremophiles which can thrive in harsh environments with low moisture, low nutrients, and high salinity where other life forms cannot. These are also resilient to high radioactive conditions due to specific physiological and molecular adaptations such as melanin production. These properties make fungi a promising and sustainable option for the bioremediation of radioactive wastewater. However, challenges such as radionuclide toxicity to fungal cells and the safe disposal of contaminated fungal biomass remain critical considerations. This chapter explores the mechanisms by which fungi mitigate radioactive contamination and discusses their potential applications in wastewater treatment, highlighting the advantages of fungal bioremediation as a scalable solution for nuclear waste management.