A new type of acid-sensitive 100% hyperbranched polyacetals (HBPA) was synthesized, which could be completely degraded into small molecules under acidic environment and avoid the accumulative toxicity in vivo. The AB(2) monomer was synthesized by 4-carboxybenzaldehyde and 2-bromoethanol. The bulk polycondensation was carried out in vacuum environment to remove water byproduct. The massive terminal aldehyde groups of HBPA were conjugated with mPEG-NH2 and doxorubicins to form amphiphilic acid-sensitive polymer-drug conjugates (DOX-HBPA-PEG). The stability of the micelles of DOX-HBPA-PEG was evaluated by DLS at different pH value in phosphate buffer saline (PBS). The DOX release in vitro showed that the cumulative release rate was 14.51% in pH 7.4 PBS after 24 h and the cumulative release rate was 48.56% in pH 6.0 PBS after 24 h. The results of cell viability of DOX-HBPA-PEG and HBPA-PEG showed that the polymer-DOX conjugates were effective drug delivery systems. The uptake process of DOX-HBPA-PEG by A549 cells showed that the micelle was totally swallowed in 1 h later. The controllable drug release nature, stability, biocompatibility and completely degradable structures (acid-sensitive) make them to be promising drug delivery systems.