DNA is generally considered to be the most critical cellular target when considering the lethal, carcinogenic and mutagenic effects of drugs, radiation and environmental chemicals. So the study aim to the determination the damaging effect of -radiation on DNA and the protective effect of deoxynucleotide triphosphates (dNTPs). The study includes three cell types, lymphocytes, kidney cells of African gree monkey (Vero) and hepatocellular carcinoma of human (HePG2) exposed to 1-5 Gy of -radiation and by using fluorometric analysis of DNA unwinding (FADU) method, DNA damage was measured after radiation. The cells were divided into two groups: The first received 5x10-5 dNTPs from 0-30 minutes after radiation, while the second group was not supplemented with deoxynucleotides. Clonogenic survival for vero and HePG2 cell lines was measured. The results revealed that the increase of irradiation dose precipitates an increase of DNA strand breaks. The slope curve of initial DNA damage and mean inactivation dose (D ) differ between vero and HepG2 cell line by a factor of up 3.5 and 2, respectively. dNTPs have clear ameliorating effect on DNA damage. FADU method can play an important role in the choice of a suitable treatment (radiation or drugs) and its dosage according to measurement of DNA damages in selective malignant tissues. Moreover, using dNTPs mixture can reduce the side effect of these treatment especially after experimentally on live mammals (mice).