The purpose of the present study was to investigate the relation of serum malondialdehyde (MDA) levels, MDA and viral burden to necroinflammation of liver and fibrosis and effects of interferon therapy on MDA in patients with chronic hepatitis B. Forty-four chronic hepatitis B patients and 44 healthy volunteers were enrolled in the study. Fifteen cases who could be treated at the authors' clinic were re-evaluated at the end of the therapy. At the end of the study, together with the serological markers relating to viral aetiology, alanin aminotransferase (ALT), aspartat aminotransferase (AST), serum MDA and hepatitis B virus-DNA (HBV-DNA) levels were determined in the study group. Histopathological findings in the liver were scored as necroinflammatory activity (grade) and fibrosis (stage) according to the Knodell scoring scale. The malondialhyde levels were significantly higher in the chronic hepatitis B patients compared to the healthy controls (p<0.05). No significant correlation could be found between MDA levels and viral burden, necroinflammation and fibrosis of the liver in the chronic hepatitis B patients (r=0.031; -0.144 and -0.009, respectively, p>0.05). However, post-treatment MDA levels were found to be significantly lower than the pre-treatment values in the patients (p<0.05). In conclusion, the present findings appear to confirm the presence of oxidative stress in chronic hepatitis B and interferon therapy inhibits this oxidative stress in the liver.