Multidrug resistance (MDR) is one of the major obstacles to successful chemotherapy.Overexpression of drug efflux transporters such as P-glycoprotein (P-gp) is an important factor responsible for the MDR.Herein, a novel copolymer, D-α-tocopheryl polyethylene glycol l000-block-poly(β-amino ester), (TPGS-b-PBAE, TP) was synthesized for overcoming multidrug resistance by synergistic effect of pH-sensitive behavior of PBAE and P-gp inhibiting activity of TPGS.