Abstract: A long chain structure of DNA(polyaptamer)composed of multiple aptamer units was synthesized by rolling circle amplification and used for the construction of polyaptamer-doxorubicin system in the treatment of leukemia cells. It was found that the system was significantly more effective than monoaptamer in targeting and killing leukemia cells as it provided 35-fold enhanced binding affinity and 10-fold greater drug loading via multivalent effects. Drug release and cell viability also proved that the conjugates could gain entrance into the cells and rapidly release doxorubicin under the action of lysosome, leading to the tumoricidal effect.