ObjectiveTo investigate the relationship between miR-34a expression and the irradiation-sensitivity of cells and tissues.MethodsRT-PCR was used to detect the miR-34a expression in different cells and tissues before and after irradiation; flow cytometry was employed to examine the apoptosis of cells and MTT assay was used to observe the cell viability. The U87MG tumor cells were transfected with miR-34a mimics to promote miR-34a expression and the cell viability was observed 24 h later. The HEK293 renal epithelial cells were transfected with miR-34a inhibitors to decrease miR-34a expression and the cells apoptosis was observed 24 h later.ResultsThe expression of miR-34a was higher in highly irradiation-sensitive cells than in lowly irradiation-sensitive cells before irradiation; the increase of miR-34a expression was greatly higher in highly irradiation-sensitive cells than in lowly irradiation-sensitive cells 24 h after irradiation. The up-regulation of miR-34a decreased the viability of U87MG tumor cells, and down-regulation of miR-34a decreased the apoptosis of HEK293 cells.ConclusionThe irradiation-sensitivity of cells is positively associated with miR-34a; cells with high irradiation-sensitivity have a greater up-regulation of miR-34a expression after irradiation. Increased miR-34a expression can noticeably increase the irradiation-sensitivity of U87MG tumor cells and decreased miR-34a expression has a irradiation prevention effect on normal HEK293 cells.