Multidrug resistance (MDR) is a common phenomenon in clinical oncology and is a major obstacle to cancer chemotherapy. Many nanoparticle (NP)-based drug delivery systems have been developed to overcome MDR depending on increasing intracellular drug concentrations via increased cellular uptake and rapid drug release. The objective of this work was to investigate the performance and possible mechanisms of enzyme-sensitive mPEGylated dendron-GFLG-DOX conjugate based nanoparticles for blockading the MDR phenotype of MCF-7/ADR. In vitro, mPEGylated dendron-GFLG-DOX conjugate based nanoparticles could significantly promote cellular uptake and accumulation, potent cytotoxicity and apoptosis compared to free DOX in resistant cells. mPEGylated dendron-GFLG-DOX conjugate based nanoparticles were found to translocate across the membranes of resistant cells via active endocytic pathways leading to more DOX accumulating in the nuclei of MCF-7/ADR cells. Importantly, we found that mPEGylated dendron-GFLG-DOX conjugate based nanoparticles could induce cathepsin B in the cytoplasm and enhance lysosomal-mediated cell death compared to free DOX. Furthermore, mPEGylated dendron-GFLG-DOX conjugate based nanoparticles enhanced the drug's penetration, toxicity, and growth inhibition compared to free DOX in the three-dimensional multicellular tumor spheroid model. In vivo, mPEGylated dendron-GFLG-DOX conjugate based nanoparticles significantly improved the therapeutic efficacy against MDR xenograft tumors, and showed better biocompatibility than free DOX. These results indicated that mPEGylated dendron-GFLG-DOX conjugate based nanoparticles could be used as an alternative drug delivery system for MDR tumor treatment through initiating the lysosomal apoptosis pathway.