Multidrug resistance(MDR) is a formidable obstacle in cancer pharmacotherapy. One of the mechanism is ATP-binding cassette(ABC) transporters overexpression in multidrug resistant tumor cells. The strategy to overcome MDR in cells expressing ABC efflux transporters is to develop the inhibitors of efflux transporters, likely reversing MDR. Furthermore, the recent studies demonstrated that the tumor stem cells may be innately resisted through the expressing efflux transporters. This provides one new therapeutic target for anti-cancer. In this review, we provide the overviews of ABC transporters in multidrug resistant tumor cells and the development of ABC transporter inhibitors.