Abstract: Radiosensitivity is a complex phenomenon in tumor cells and there exist special biological effects in different types of tissues' cells in inadiation-induced cell responses. Tumor radiosentivity is tightly connected with irradiation-induced apoptosis and is regulated by many protein products of apoptosis-related genes such as p53 and related proteins, Bcl-2 gene family proteins, Fas and sphingomyelin/ceramide-mediated signalling pathways and caspases cascade etc.