The aim of this study was to investigate the effect of ferrocene (FeCp 2 ) and ferrocenium salt (FeCp 2 BF 4 ) on the viability of MCF7 breast cancer and MCF10A non-tumorigenic epithelial cells and the role of Reactive Oxygen Species (ROS) production in cell cytotoxicity.FeCp 2 BF 4 displayed higher cytotoxicity than FeCp 2 , and the cell type contributes toward complexes toxicity, as MCF7 cells displays greater toxicity than MCF10A cells.The mechanism of toxicity seems to involve the generation of ROS, with MCF7 cells producing higher levels than epithelial cells.In addition, the inhibition of ROS was found to be protective against ferrocene induced cell death.The findings of cancerous cell-induced cytotoxicity by ROS indicate a potential utility of ferrocenyl derivatives in the treatment of cancer.