In this work, we report an amperometric immunosensor for detecting Hepatitis B surface antigen based on ChitosanFerrocene-Ammoniated multiwalled carbon nanotubes (CS-Fc-AMWNTs). The CS-Fc-AMWNTs nanocomposites were produced by Schiff base reaction, providing not only large specific surface area, but also favorable conductivity and outstanding biocompatibility. HBsAb was modified on electrode surface by glutaraldehyde cross-linking. The immunocomplex was produced after incubation with HBsAg, which hindered the electron transfer and concentration of antibody was observed to change in the current. The immunosensor showed great linear range from 1-250 ng/mL. Results from this study show that the immunosensor has good reliability and high sensitivity for detection of HBsAg in certain clinical application value.