Objective To investigate the serum interleukin-33( IL-33) level in patients with chronic hepatitis B,and to explore the correlation of serum IL-33 with hepatitis B virus( HBV) DNA load and alanine aminotransferase( ALT) level. Methods A total of 119 patients with chronic hepatitis B and 131 healthy controls were enrolled in this study. Serum levels of IL-33 were determined by enzyme-linked immunosorbent assay. For patients with chronic hepatitis B,HBV DNA loads were quantified by real-time quantitative PCR,while ALT levels were measured by continuous monitoring assays. The t test was applied in the comparison of continuous data. The Pearson correlation analysis was used to investigate the correlation of serum IL-33 level with HBV DNA load and ALT level. Results Serum levels of IL-33 were significantly higher in patients with chronic hepatitis B( 62. 7 ± 29. 3 ng / ml) than in healthy controls( 16. 4 ± 4. 5 ng / ml)( t =17. 02,P < 0. 01). Serum IL-33 level was negatively correlated with log10[HBV DNA]( r =-0. 703,P < 0. 01) but positively correlated with ALT( r = 0. 324,P < 0. 01) in patients with chronic hepatitis B. Conclusion This study suggests that IL-33,an immune stimulator,may play a role in inhibiting HBV replication in patients with chronic hepatitis B.