AIM: To evaluate the effect of combined antisense oligonucleotides targeting midkine (MK-AS) and chemotherapeutic drugs [cisplatin(DDP), 5-fluorouracil(5-FU) and adriamycin (ADM)] on inhibition of HepG2cell proliferation, and to analyze the efficacy of MK-AS used in combined ADM in in situ human hepatocellular carcinoma (HCC) model.METHODS: HepG2 cells were treated with MK-AS and/or chemotherapeutic drugs mediated by Lipofectin,and cell growth activity was determined by MTS assay.An in situ HCC model was used in this experiment. MKAS, ADM and MK-AS + ADM were given intravenously for 20 d, respectively. The animal body weight and their tumor weight were measured to assess the effect of the combined therapy in vivo.RESULTS: Combined treatment with MK-AS reduced the IC50 of DDP, 5-FU and ADM in HepG2 cells. MK-AS significantly increased the inhibition rate of DDP, 5-FU and ADM. Additionally, synergism (Q 1.15) occurred at a lower concentration of ADM, 5-FU and DDP with combined MK-AS. Combined treatment with MK-AS and ADM resulted in the more growth inhibition on in situ human HCC model compared with treatment with chemotherapeutic drugs alone.CONCLUSION: MK-AS increases the chemosensitivity in HepG2 cells and in situ human HCC model, and the combination of MK-AS and ADM has a much better in vitro and in vivo synergism.