Background : Hepatitis B virus(HBV) is an important mediates of chronic liver cirrhosis and hepatocellualr carcinoma. HBV DNA quantification is used to establish the prognosis of chronic HBV-related liver disease, to identify those patients who need to be treated, and to monitor the virologic response and resistance to antiviral therapies. Real-time PCR-based assays are gradually replacing other technologies for routine quantification of HBV DNA in clinical practice. The goal of this study was to evaluate the intrinsic characteristics and clinical performance of the real-time PCR Cobas AmpliPrep/Cobas TaqMan(CAP/CTM) platform for HBV DNA quantification. Methods : Patient serum referred to Neodin Medical Institute for determine HBV DNA were used for this assay. DNA was extracted by CAP system(Cobas AmpliPrep, Roche Co, USA) from patient serum. The accuracy, precision, and linearity were determined using CTM(Cobas TaqMan)/HBV real time PCR kit. For comparison test, HBV bDNA assay(Siemens Co., Germany) and home brew kit were used. Results : The limit of detection of CAP/CTM was 15 IU/mL and clinical specificity was 99%. Quantification was linear over the full dynamic range of quantification of the assay(r²=0.986) and was not affected by dilution. Analyses of the mean intra- and inter -assay imprecision within the linear range of quantification showed a coefficient of variation of <10% and <10%, respectively. When comparing HBV DNA levels measured in the same individuals with CAP/CTM HBV real time PCR and HBV bDNA and home brew kit were r²=0.9817 and r²=0.9568, respectively. Conclusion : The CAP/CTM HBV DNA assay is sensitive, specific, and reproducible, and it accurately quantifies HBV DNA levels in patients chronically infected by HBV. Samples with HBV DNA concentrations above the upper limit of quantification need to be diluted and then retested. Broad use of fully automated real-time PCR assays should improve the management of patients with chronic HBV infection.