Elacridar (ELC), a reversal agent of multidrug resistance (MDR), has been demonstrated as an excellent P-glycoprotein (P-gp) inhibitor which could reverse P-gp mediated drug efflux[1].However, low solubility and poor stability of ELC limited its use in cancer treatment.To address this issue, a redox and pH dual sensitive nanocarrier (PSSP) was constructed by introducing disulfide bond to link the polyethylene glycol (PEG) and polyamidoamine (PAMAM)[2] to co-deliver doxorubicin (DOX) and ELC,DOX and ELC were encapsulated into the hydrophobic cavity of PSSP to form co-loading nanoparticles PSSP/DOX/ELC.