Mitochondria are emerging as intriguing targets for anti-cancer agents. We tested here a novel approach, whereby the mitochondrially targeted delivery of anti-cancer drugs is enhanced by the addn. of a triphenylphosphonium group (TPP+). A mitochondrially targeted analog of vitamin E succinate (MitoVES), modified by tagging the parental compd. with TPP+, induced considerably more robust apoptosis in cancer cells with a 1-2 log gain in anti-cancer activity compared to the unmodified counterpart, while maintaining selectivity for malignant cells. This is because MitoVES assocs. with mitochondria and causes fast generation of reactive oxygen species that then trigger mitochondria-dependent apoptosis, involving transcriptional modulation of the Bcl-2 family proteins. MitoVES proved superior in suppression of exptl. tumors compared to the untargeted analog. We propose that mitochondrially targeted delivery of anti-cancer agents offers a new paradigm for increasing the efficacy of compds. with anti-cancer activity.