Abstract: In this study, pig IL-2 eukaryotic expression plasmid pcDNA-IL-2 was constructed and its adjuvant effect was investigated. Four groups of pigs were immunized with sterilized water, empty vector pcDNA3.1(+), PRRSV-SC2-OFR5 gene eukaryotic expression plasmid pcDNA-PRRSV-SC2-ORF5 and a mixed solution of pcDNA-IL-2 and pcDNA-PRRSV-SC2-ORF5 respectively. Serum of pig in each group was collected at different time post inoculation, and antibody to PRRSV was measured by ELISA. Peripheral T lymphocytes were acquired from a small quantity of blood of each pig, and the activity of lymphocyte proliferation was detected by MTT methods after being cultured with RPMI1640 culture medium. Content of CD+4and CD+8 of peripheral T lymphocytes in each groups of pigs were tested by cytospectrometry. Results showed that the antibody and peripheral T lymphocytes level, content of CD+4,CD+8 cell of the pigs immunized with both pcDNA-IL-2 and pcDNA-PRRSV-SC2-ORF5 were significantly higher than that of the pigs immunized with pcDNA-PRRSV-SC2-ORF5 alone, indicate that plasmid pcDNA-IL-2 can be used as a adjuvant to enhance PRRS gene vaccine.