In the present study, a novel pH-responsive amphiphilic copolymer, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] conjugated poly(β-amino esters) (DSPE-b-PEG-b-PAE-b-PEG-b-DSPE), was designed and successfully synthesized via Michael-type step polymerization. The chemical structure of the pentablock copolymer was confirmed with proton nuclear magnetic resonance (1H-NMR) and Fourier transform infrared (FT-IR) spectroscopy. The copolymer was able to self-assemble into core/shell polymeric micelles in aqueous solution at low concentrations, and its critical micelle concentration (CMC) value was 4.5 mg l−1 determined by fluorescence spectrophotometry. The pKb value of the copolymer was about 6.5, confirmed by acid–base titration, indicating the pH-sensitivity of the polymeric micelle. The hydrodynamic diameter, distribution and zeta potential of the polymeric micelles at different pH conditions were monitored by dynamic light scattering (DLS). Doxorubicin (DOX) was encapsulated into the core of the micelles with a high drug loading content (15.9%) and entrapment efficacy (60.4%). In vitro experiments demonstrated that the release behaviour of DOX from the DOX-loaded polymeric micelles (DOX-PMs) was pH-triggered. When the pH decreased from 7.4 to 5.0, the drug release rate was markedly accelerated. MTT assay showed that the copolymer had negligible cytotoxicity whereas the DOX-PMs displayed high toxicity for tumour cells such as B16F10, HepG2 and HeLa cell lines. The results demonstrated that these pH-sensitive polymeric micelles could be used as potential anti-cancer drug carriers for cancer chemotherapy with controlled release.