Novel redox-responsive polyphosphate nanosized assemblies based on amphiphilic hyperbranched multiarm copolyphosphates (HPHSEP-star-PEPx) with backbone redox-responsive, good biocompatibility, and biodegradability simultaneously have been designed and prepared successfully. The hydrophobic core and hydrophilic multiarm of HPHSEP-star-PEPx are composed of hyperbranched and linear polyphosphates, respectively. Benefiting from the amphiphilicity, HPHSEP-star-PEPx can self-assemble into spherical micellar nanoparticles in aqueous media with tunable size from about 70 to 100 nm via adjusting the molecular weight of PEP multiarm. Moreover, HPHSEP-star-PEPx micellar structure can be destructed under reductive environment and result in a triggered drug release behavior. The glutathione-mediated intracellular drug delivery was investigated against a HeLa human cervical carcinoma cell line, and the results indicate that doxonibicin-loaded (DOX-loaded) HPHSEP-star-PEPx micelles show higher cellular proliferation inhibition against glutathione monoester pretreated HeLa cells than that of the nonpretreated ones. In contrast, the DOX-loaded micelles exhibit lower inhibition against buthionine sulfoximine pretreated HeLa cells. These results suggest that such redox-responsive polyphosphate micelles can rapidly deliver anticancer drugs into the nuclei of tumor cells enhancing the inhibition of cell proliferation and provide a favorable platform to construct excellent drug delivery systems for cancer therapy.