Abstract: In order to study the effect of cell mediated immunity regulation of duck IFN-α eukaryon expression plasmid (pcDNA-SDIFN-α) on DPV attenuated vaccine in ducks , pcDNA-SDIFN-α was administrated to 28-day old ducks at the dose of 1, 3, 6 μg/duck, respectively, by gene-gun. PBS and empty vector pcDNA were used as control.15 days later, all ducks were injected with DPV attenuated vaccine, and blood samples were collected at 3, 7, 14, 21, 28, 35, 49, 63, 84 days after injection. T lymphocyte proliferation tests (MTT) were used to detect the T-lymphocyte proliferation in peripheral blood(PBL) of ducks. Blood samples collected at 7, 14, 21, 28, 35, 49 days were detected by fluorescence activated cell sorter (FACS) for recording the number of CD+3 T lymphocytes of ducks Results were as follows: ① Reaction of T lymphocytes in PBL to ConA (OD value)of ducks treated with pcDNA-SDIFN-α were higher than that of PBS and pcDNA control groups in 3—84 days. There were highly significant difference between 1 μg/duck group and two control groups in 3—84 days (P≤0.01), between 3 μg/duck group and two control groups in 3-84 days (P≤0.01,P≤0.05), and between 6 μg/duck group and two control groups in 7-49 days (P≤0.01,P≤0.05).The significant difference was also present between 1 μg/duck and 3,6 μg/duck groups in 3-35 days(P≤0.05). Moreover, there was no significant difference between 3 μg/duck group and 6 μg/duck group (P≥0.05). pcDNA control group was higher than PBS control group, but no difference was found (P≥0.05).②Change of the number of CD+3 T-lymphocyte of ducks administrated with different doses of pcDNA-SDIFN-α were higher than that of PBS and pcDNA control groups in 7-49 days.1 μg/duck group was significantly higher than PBS and pcDNA control groups in 14-49 days (P≤0.01), there were significant difference between 3 μg/duck group and two control groups in 21-49 days (P≤0.01,P≤0.05),significant difference between 6 μg/duck group and two control groups in 7-49 days (P≤0.01,P≤0.05). No significant difference was found among the groups of 1, 3, 6 μg/duck (P≥0.05).There was no significantly difference between two control groups(P≥0.05). The results indicate that pcDNA-SDIFN-α administrated 15 days before injection of DPV attenuated vaccine could significantly enhance cellular immunity induced by DPV attenuated vaccine. pcDNA-SDIFN-α is an excellent DPV attenuated vaccine molecular adjuvant, best result could be obtained with the dose of 1 μg/duck of pcDNA-SDIFN-α inoculated by gene-gun.