Cancer cells have worked out numerous strategies to escape cell death through the extrinsic pathway,so anticancer drugs directly targeting mitochondria hold great potential to get around the resistance mechanisms that have developed towards conventional chemotherapeutics.However,large amounts of mitochondria-targeting anticarcinogens are obtained from natural compounds and have been discovered by chance rather than by systematic screening [1].Developing methods aimed at specifically distinguishing mitochondria-targeting drugs from large quantities of natural materials or synthetic compounds will present a treasure trove for anticarcinogen discovery.Employing mitochondrial membrane potential loss as an early apoptotic marker,we have established a novel strategy to identify whether anticancer drugs induce apoptosis by directly targeting mitochondria.In our work,Rhodamine 123,a cationic dye that emits green fluorescence,was used to monitor the membrane potential of mitochondria isolated from HeLa cells.A laboratory-built high-sensitivity flow cytometer was applied to measure the side scatter and fluorescence signals of individual mitochondria before and after compound treatment.Anticancer drugs such as staurosporin,betulinic acid,paclitaxel,ABT-737,curcumin and CCCP were tested.The results indicated that betulinic acid,ABT-737 and paclitaxel could directly target mitochondria,while others could not,which was in accordance with the literature reports.Given that the rate of anticancer drug discovery and mechanism of drug action can profoundly affect the progress of cancer therapy,we believe that our method could not only provide a rapid and efficient way for drug screening but also open a new channel to study the mechanism of anticancer drugs related to mitochondria-mediated apoptosis pathway.