Background: High-mobility group box 1 (HMGB1), identified as an alarmin molecule, was shown to have a role in virus-triggered liver injury. We aimed to evaluate the association between serum levels of HMGB1 and liver fibrosis. Method: This cross-sectional case-control study included 189 chronic hepatitis B (CHB) patients and 51 healthy controls. All patients underwent liver biopsy and modified Knodell scoring system used to determine the fibrosis level in CHB patients. Serum HMGB1 levels were determined with enzyme-linked immunosorbent assay (ELISA). Results: Mean serum HMGB1 levels of patients (58.1 ± 54.7) were found to be higher than those of the control group (7.1 ± 4.3) (P = .001). HMGB1 levels of patients with advanced-stage fibrosis (stage 4 and 5) were detected to be higher than those of patients with early-stage fibrosis (stage 1-3). However, this difference was not statistically significant (P >. .05). Albumin levels of fibrosis 3 and 4 patients were lower than fibrosis 1 and 2 patients. ALT, HBV DNA, and AFP levels of fibrosis 5 patients were significantly higher than fibrosis 1 and 2 patients, and their platelet and albumin levels are lower than fibrosis 1 and 2 patients (P < .001). In a logistic regression model, fibrosis levels were correlated with ALT values and inversely correlated with albumin levels. Conclusion: In this study, we demonstrated that serum HMGB1 levels increase in the early course of liver injury and this increase is not correlated with severity of the liver damage.