We previously reported that $IFN-{gamma}$ producing T cell responses induced by the combined therapy of DNA vaccine and lamivudine for one year are important for the induction of sustained virological response (SVR). However, $IFN-{gamma}$ production is not sufficient to predict sustained viremia control in chronic hepatitis B (CHB) carriers treated. Methods: Twelve CHB carriers were intramuscularly immunized 12 times at a 4-week interval with 8mg of HBV DNA vaccine during the standard lamivudine treatment (100mg/daily/1 year). The level of cytokines during and after the combined therapy in plasma of all 12 CHB carriers treated was determined by each ELISA kit. Six out of 12 CHB carriers revisited the clinic, and their HBV DNA levels were examined. Results: The combined therapy increased plasma IL-12 and IL-12/p40 ratio during the treatment (baseline vs. peak level: $41.8{pm}8.3$ vs. $163.1{pm}29.2;pg/ml$; p<0.01 and $0.96{pm}0.25$ vs. $3.58{pm}0.86$; p<0.01, respectively), and the peak level of plasma IL-12 and IL-12/p40 ratio was evoked at 6 to 10 months during the combined therapy. In particular, CHB carriers with SVR had two and three-fold higher level of the peak plasma IL-12 and plasma IL-12/p40 ratio than non-virological responders (NVRs), respectively ($218.0{pm}41.4$ vs. $108.1{pm}28.6;pg/ml$; p=0.09 and $5.35{pm}1.38$ vs. $1.80{pm}0.29$; p<0.05, respectively), while p40 level was consistent during the combined therapy. In addition, there was no significant temporal correlation between the peak IL-12/p40 ratio and the elevation of serum alanine amino-transferase (ALT) in this study, contrast to $IFN-{alpha}$ therapy which induced peak IL-12 level following ALT flares. Conclusion: Our results indicate that the combined therapy induces the increase of plasma IL-12 and IL-12/p40 ratio, which are associated with long-term SVR in CHB carriers.