A novel polyethylenimine(PEI)-based gene carrier was used for carrying a plasmid encoding small interfering RNA(siRNA). A series of semicrystalline copolymers

especially with functional group carboxyl poly(L-lactide-co-β-malic acid) were synthesized. Random polymers P(LA-co-BMD) were first synthesized through ring-opening copolymerization of L-LA and 3(S)-[(Benzyloxycarbony) methyl]-1

4-dioxane-2

5-dione(BMD) in the presence of dodecanol as initiator and stannous octoate(Sn(Oct)

2

) as catalyst. The structure of the copolymers was characterized by Nuclear Magnetic Resonance (1H NMR)

Gel Permeation Chromatography ( GPC)

and Differential Scanning Calorimetry ( DSC). The density of carboxyl groups were increased with the functional monomer. The PEI was coupling with the copolymer by amino groups. The modification of polymeric vectors has shown higher transfection efficiency and lower cytotoxicity. The micelles showed a significant reduction in surface zeta-potential ( — 9〜-35mV) and a much smaller particle size(50〜500nm).