We present here a facile strategy for constructing Dextran-poly(3-acrylamidophenylboronic acid) (Dextran-PAPBA) nanoparticles (NPs) through a radical polymerization of the monomer 3-acrylamidophenylboronic acid (APBA) bound by dextran via a boronic acid-diol reaction in aqueous solution. The synthesized Dextran-PAPBA NPs are stable in a wide pH range. Their size and composition are tunable by varying the feeding molar ratio of the glucopyranoside unit in dextran to APBA. Additionally, the NPs have good biocompatibility and cell membrane penetrability, as demonstrated by in vitro experiments. Doxorubicin was encapsulated in the NPs and exhibited a sustained and strongly pH-dependent release profile that would greatly favor the in vivo drug delivery performance of the NPs. The facility of this strategy together with the tunable boron content and outstanding drug release and cellular membrane crossing performance of the produced NPs should greatly boost their applications in boron neutron capture therapy (BNCT) and chemotherapy for cancer treatment.