In the present study, the in vitro cytotoxicity of daidzein was evaluated in human BEL-7402, A549, HeLa, HepG-2 and MG-63 cancer cell lines. BEL-7402 cells were sensitive to daidzein treatment, with an IC50 value of 59.7±8.1 µM. Daidzein showed no cytotoxic activity toward A549, HeLa, HepG-2 and MG-63 cells. Daidzein increased the levels of reactive oxygen species (ROS) and induced a decrease in mitochondrial membrane potential. Morphological and comet assays showed that daidzein effectively induced apoptosis in BEL-7402 cells. Additionally, daidzein caused cell cycle arrest at the G2/M phase in the BEL-7402 cell line. Daidzein downregulated the expression of Bcl-2, Bcl-x and Baid proteins and upregulated the levels of Bim protein in the BEL-7402 cells. The results demonstrated that daidzein induced BEL-7402 cell apoptosis through an ROS-mediated mitochondrial dysfunction pathway.