BACKGROUND: Hepatocellular carcinoma(HCC) is one of the most common cancers worldwide. Most of the patients with HCC lose the surgical opportunity at the time of diagno sis. Some novel therapeutic modalities, like gene therapy, are promising for the treatment of HCC. However, the success of gene therapy depends on two aspects: efficient gene materials and gene delivery vectors. The present study was to develop new chitosan-based nanoparticles for a midkine-si RNA(anti HCC gene drug) delivery.METHODS: The novel gene delivery vector(MixN CH) was syn thesized by hybrid-type modification of chitosan with 2-chloro ethylamine hydrochloride and N, N-dimethyl-2-chloroethylamine hydrochloride. The chemical structure of Mix NCH was char acterized by FT-IR and 1HNMR. The cytotoxicity of Mix NCH was determined by MTS assay. The gene condensation ability and size, zeta potential and morphology of Mix NCH/MK si RNA nanoparticles were measured. The in vitro transfection and gene knockdown efficiency of midkine by Mix NCH/MK si RNA nanoparticles was detected by q RT-PCR and Western blotting. Gene knockdown effect at the molecule level on the proliferation of Hep G2 in vitro was determined by MTS assay.RESULTS: Mix NCH was successfully acquired by aminoalkyl ation modification of chitosan. The Mix NCH could condense MK-siR NA well above the weight ratio of 3. The average size of Mix NCH/MK-si RNA nanoparticles was 100-200 nm, and thesurface charge was about +5 m V. Morphologically, Mix NCH/MK-si RNA nanoparticles were in regular spherical shape-with no aggregation. Regarding to the in vitro transfection of nanoparticles, the MixN CH/MK-siR NA nanoparticles reduced MK m RNA level to 14.03%±4.03%, which were comparable to Biotrans(8.94%±3.77%). Mix NCH/MK-si RNA effectively inhibited the proliferation of Hep G2 in vitro.-CONCLUSION: Mix NCH/MK-si RNA nanoparticles could be effective for the treatment of hepatocellular carcinoma.-