Chronic hepatitis B virus (HBV) infection is associated with impairment of HBV-specific immune responses. Recently, it has been shown that regulatory T (Treg) cells downregulate HBV-specific immune responses but their role in chronic hepatitis B is still controversial. We hypothesized that liver injury enhances the influence of Treg cells on HBV-specific immune responses. The frequency of Treg cell and the in vitro expansion of HBV-specific CD8+ T cell detected by the tetramer method were investigated in 79 patients with chronic hepatitis B. Thirty-three healthy volunteers were enrolled to measure the frequency of Treg cell as controls. The results showed that in chronic hepatitis B cases, the frequency of Treg cells in peripheral blood was significantly higher than that in normal volunteers. The higher level of serum transaminase was associated with higher frequency of Treg cells, which both had a linear correlation relationship. HBV-DNA level, HBe status, age and sex had no statistical association with Treg cell frequency. Furthermore, in patients with higher serum transaminase levels, the expansion of HBV-specific CD8+ T cells was higher after removal of Treg cells when compared with patients with lower serum transaminase levels. In conclusion, our data indicate a significant association between serum transaminase level and frequency/activity of Treg cells. Based on this observation, we propose that liver-injury enhances Treg cell frequency/activity in chronic hepatitis B patients.