Dextran catches increasing attentions as a drug carrier because of its biocompatibility, biodegradability and ease of modification. In this study, we synthesized the derivated dextran by grafting with 1-(3-aminopropyl) imidazole. The dextran-based nanoparticles with sizes of < 200 nm were successfully prepared by nanoprecipitation, and its pH-sensitivities were investigated. The samples were fully characterized by FTIR, 1H NMR, SEM, AFM and Zetasizer.