The conventional chemotherapeutic agent doxorubicin hydrochloride (DOX·HCl) is often accompanied by drug resistance which has severely hindered its clinical application. By taking advantage of the self-assembled behavior of amphiphilic polyphosphazenes, we constructed novel polymersomes loading DOX·HCl or desalted DOX with chloroquine phosphate (CQ) as a drug resistance-reversal agent at 1:1 or 2:1 weight ratios via a one-step common dialysis method. The cytotoxicity evaluation of this dual drug-loaded polymersome was performed on DOX-resistant MCF-7/Adr breast cancer and HL60/Adr leukemia cells. Simultaneously, to simulate in vivo cancerous tissue, 3D tumor spheroid was constructed for tissue penetration and anti-cancer effect evaluation. As a result, PEP-DHC-1 containing DOX·HCl and CQ at 1:1 weight ratio exhibited the strongest toxicity. Furthermore, the in vivo tumor inhibition study carried out on a zebrafish xenograft model also validated that PEP-DHC-1 made the outstanding contribution to improve the sensitivity of MCF-7/Adr breast cancer to chemotherapeutics. These findings suggest that this DOX·HCl and CQ co-delivery system based on PEP polymersomes might be promising for drug resistance reversal of cancer therapy and consequently enhanced anti-cancer efficacy.