This study is try to investigate the positive ratio of the mitochondrial DNA (mtDNA) 4934bp deletion in normal human population and if this deletion could be induced by ionizing radiation. 109 normal human peripheral blood samples were collected and analyzed for the mtDNA 4934bp spontaneous deletion by PCR. 3 samples of human normal peripheral blood with mtDNA 4934bp spontaneous deletion were exposed to 0, 2 and 6Gy ,60,Co γ-rays ,in vitro, and the analysis of the mtDNA 4934bp deletion was made after exposure. Finally, semi-quantification PCR was used to analyze the 4934bp deletion level after 0, 2 and 6Gy irradiation with normal peripheral blood samples. The results show that 45/109 or 41% of normal human peripheral blood samples have spontaneous 4934bp deletion, and the BLAST results are proved that the 4934bp deletion locates in nt8435-nt13368 on heavy strand. The spontaneous deletion rate increases with the age (,p,<,0.01). The 4934bp deletion is detected in peripheral blood samples before and after irradiation and the 4934bp deletion level is 2,3, 2,5, and 2,7, respectively at the irradiation dose of 0, 2 and 6Gy. These observations suggests that it would be a normal case of spontaneous 4934bp deletion in normal human peripheral blood, and the 4934bp deletion level could be enhanced along with the dose of ionizing radiation.