Combined with chemiluminescence-immunoassays, HBsAg in human body can be quantitatively detected by using antibody-labeled magnetosomes. 50 serum samples from hepatitis B patients are detected by using double antibody sandwich method which includes using monoclonal antibody to label magnetosomes, polyclonal antibody to label alkaline phosphatase, dioxetanephosphate as luminous substrates. Results show that 20 people are hepatitis B patients, 30 people are hepatitis B carriers merely. Besides, compared with ELISA, 50 random human serum samples are detected. Among 4 kinds of label methods, the one using double function reagent, SPDP, to couple antibody and magnetosomes is the best. And then the method of quantitative detection of HBsAg with chemiluminescence-immunoassays is established. The threshold of sensitivity of this method in detecting antigens is 0.1 ng/ml, which completely accords with the results obtained by using standard specific serum samples that provided by National Institute For The Control of Pharmaceutical and Biological Products. Among 100 clinical samples detected by this method, there are 20 hepatitis B patients and 30 hepatitis B carriers, which is 100% consistent with the results obtained by ELISA. While used to detect 50 random human serum samples, this method is better than ELISA because of its higher sensitivity. Results show that this method can be used in the early detection of HBsAg because of its high sensitivity, strong-specificity, good quantitative accuracy.