Multidrug resistance (MDR) is the major cause for chemotherapy failure, which constitutes a formidable challenge in the field of cancer therapy. The synergistic chemo-photothermal treatment has been reported to be a potential strategy to overcome MDR. In this work, rationally designed enzyme-degradable, hyper branched polyphosphoester nanomedicines were developed for reversing MDR via the codelivery of doxorubicin and IR-780 (hPPE(DOX&IR)) as combined chemo-photothermal therapy. The amphiphilic hyperbranched polyphosphoesters with phosphate bond as the branching point were synthesized via a simple but robust one-step polycondensation reaction. The self-assembled hPPE(DOX&IR) exhibited good serum stability, sustained release, preferable tumor accumulation, and enhanced drug influx of doxorubicin in resistant MCF-7/ADR cells. Moreover, the degradation of hPPE(DOX&IR) was accelerated in the presence of alkaline phosphatase, which was overexpressed in various cancers, resulting in the fast release of encapsulated doxorubicin. The enzyme-degradable polymer generated synergistic chemo-photothermal cytotoxicity against MCF-7/ADR cells and, thus, the efficient ablation of DOX-resistant tumor without regrowth. This delivery system may open a new avenue for codelivery of chemo- and photothermal therapeutics for MDR tumor therapy.