Amphiphilic polymer nanoparticles have attracted considerable attention especially as anticancer drug delivery system, since they can enhance bioavailability and reduce side effects of drugs used for chemotherapy. Novel poly (3-hydroxybutyric-co-3-hydroxyvaleric, PHBV)/dextran nanoparticles (PDNPs) drug delivery system was formulated via an original double emulsion (w1/o1/w2) solvent-evaporation method. The mean diameter of PDNPs was 205.0±6.9 nm and their zeta potential was -1.59±0.12 mV by using dynamic light scattering (DLS) detection. PDNPs showed obvious core-shell structure with uniform particle dispersion. Cisplatin, as a model anticancer drug, was loaded to demonstrate the characterizations of the drug delivery system, and its loading did not significantly alter the hydrodynamic diameter and zeta potential of nanoparticles with 19.3±2.9% of drug loading content (DLC).In-vitro drug release profile of cisplatin from cisplatin-loaded PDNPs found that it can be released faster in normal cells (pH=7.4) than cancer cells (pH=5.5) in phosphate buffered saline (PBS), and the release period was more than 7 d,which demonstrated that this drug delivery system was pH-responsive and with excellent slow-release performance. PDNPs displayed no cytotoxicity, and cisplatin-loaded PDNPs exhibited higher killing efficient to cancer cells when compared with normal cells, which indicated this nano-delivery system can kill cancer cells more effectively.Thus, the novel PDNPs drug delivery system can be potentially applied for cancer chemotherapy, which will improve the utilization ratio and reduce side effect of drugsin the cancer chemotherapy.