Objective To investigate the possible effects on radiosensitivity in human umbilical vein endothelial cells after transfection of pcDNA3.1+Ape1 plasmid. Methods The expressing vector pcDNA3.1+ Ape1, the control vector pcDNA3.1+or non-transfection cells was irradiated by 2, 4, 6, and 8 Gy photon beam at 48 h post-transfection. The value of initial and residual Oliver tail moment (OTM) under the alkaline single cell gelelectrophoresis assay and the colony forming test were utilized as the markers for the evaluaton of cells intrinsic radiosensitivity. The effect on radiosensitivity in human umbilical vein endothelial cells after transfection of the expressing vector pcDNA3.1+Ape1 was analyzed according to the radio-dose, compared to the empty vecor control and non-transfection cells. Results The initial and residual OTM value of endothelial cells transfected by 3 μg pcDNA3.1+Ape1 plasmid was lower significantly than ones of endothelial cells untransfected at 2 Gy irradiation (P<0.01), but was no significant difference at 8 Gy (P>0.05), and SF2 was higher remarkably in transfected cells than one in untransfected cells (P<0.05), but SF4, SF6 and SF8 were no significant differences (all of P>0.05). Conclusions The transfection of pcDNA3.1+Ape1 plasmid could enhance radioresistance of endothelial cells to the low-dose irradiation.