Good blood compatibility and long-term circulation are very important to polycationic systemic gene vectors. In this work, polysulfobetaine-modified low molecular weight polyethyleneimine (LMW PEI, 1.8k) was synthesized and investigated as a vector for gene delivery in vitro and in vivo. PHEAA-b-PMPDSAH was synthesized via atomic transfer radical polymerization method, and then LMW PEI was grafted to PHEAA-b-PMPDSAH by an amido-hydroxy reaction. Incorporation of PMPDSAH into PEI was shown to retain the uncompromised ability to condense DNA into nanocomplexes. MU assays revealed that the cytotoxicity of LMW PEI-PHEAA-b-PMPDSAH/DNA complexes was lower than that of PEI (25k)/DNA and LMW PEI-PHEAA/DNA complexes. LMW PEI-PHEAA-b-PMPDSAH(50) was much superior to PEI (25k) in mediating gene transfection in the presence of 10% serum. At higher serum contents, the transfection of LMW PEI-PHEAA and PEI (25k) was deteriorated, whereas LMW PEI-PHEAA-b-PMPDSAH(50) still retained better transfection efficiency, 8-fold more effective than PEI (25k). The expression of red fluorescence protein (RFP) was evaluated by small animal in vivo fluorescence imaging system and the results showed that the expression of RFP was much higher in the mice injected with LMW PEI-PHEAA-b-PMPDSAH(50)/pDNA-RFP than with LMW PEI-HEAA/pDNA-RFP. Both in vitro and in vivo results suggested that LMW PEI-PHEAA-b-PMPDSAH(x) copolymer holds a great potential as a vector for systemic gene therapy. (c) 2013 Elsevier Ltd. All rights reserved.