Mitochondrial ion channels of the inner membrane play an important role in modulating mitochondrial membrane potential and, as a consequence, the release of reactive oxygen species (ROS) at the level of respiratory chain complexes. ROS in turn can trigger opening of the permeability transition pore and thus lead to the release of cytochrome c and other pro-apoptotic factors from mitochondria, inducing apoptosis. Specific modulation of several mitochondrial potassium channels has been linked to the regulation of apoptosis in vitro. We have recently provided evidence that, by directly acting on a mitochondrial potassium channel, specific channel inhibitors could efficiently kill different types of cancer cells (provided the channel is expressed) that are normally chemoresistant. Mutations of the tumor suppressor p53 and downregulation of pro-apoptotic Bax and/or upregulation of the expression of anti-apoptotic proteins of the Bcl-2 family are known to contribute to chemoresistance. However, these channel modulators, by acting on proteins in the inner mitochondrial membrane, bypass the necessity of upstream pro-apoptotic events such as p53 activation and Bax migration to mitochondria in order to induce release cytochrome c. Since several mitochondrial channels are overexpressed in cancer cells, their specific regulation can lead to substantial ROS release especially in the cancer cells, leading to selective cell death of the pathologic cells versus the healthy ones, according to the ROS rheostat model. In vivo evidence in animal models for melanoma, pancreatic ductal adenocarcinoma and chronic lymphocytic leukemia underlines the usefulness of exploiting mitochondrial ion channels as oncological targets.