BALB/c mice were immunized with 50 μg,100 μg,200 μg of pcDNA-PRRSV-ORF5 DNA vaccine respectively by intramuscular injection,with PBS and pcDNA3.1(+)as controls.Fluorescence activated cell Sorter (FACS)was used to detect the number of CD4+ and CD8+T-lymphocytes.T-lymphocyte proliferation test was used to detect proliferation of the T-lymphocyte cells in peripheral blood lymphocytes of mice vaccinated with pcDNA-PRRSV-ORF5 DNA vaccine.The results showed that the difference in ConA response to T-lymphocytes in blood was highly significant between all experimental groups and the control group(P＜0.01).The number of CD4+T-lymphocytes in experimental groups was significantly higher than that of the control group 7d after vaccination.The number of CD8+ T-lymphocytes in the experimental groups was higher than that of the control group 28 d after vaccination.Mice immunized with a higher dose(200 μg)of DNA vaccine demonstrated higher cellular immune response than those immunized with a lower dose(100 μg,50 μg)of DNA vaccine.The results demonstrated that pcDNA-PRRSV-ORF5 DNA vaccine could induce a good cellular immune response which may be dose-dependent.