The immune system plays important roles in determining the outcomes of hepatitis B virus (HBV) infection. Interleukin-27 (IL-27) is a recently identified pro-inflammatory cytokine produced by macrophages, dendritic cells, and epithelial cells. To determine the correlation between HBV infection and IL-27 expression, we investigated the serum IL-27 levels in patients with HBV infection and in healthy individuals. Results showed that IL-27 was significantly elevated in patients as compared to healthy individuals (P<0.001). IL-27 was also detected at higher levels in patients with liver cirrhosis or hepatocellular carcinoma than those with acute hepatitis B or chronic hepatitis B (P<0.05). We also found that IL-27 expression was influenced by HBV e antigen. In addition, our in vitro studies demonstrated that IL-27 promoter activity, mRNA and protein expression were all stimulated in cells transfected with infectious HBV clone.