Simultaneous positivity of Hepatitis B antigen and antibody may be caused by the presence of chronic Hepatitis B virus infection, infection with different subtypes of Hepatitis B virus and Hepatitis B vaccination or Hepatitis B immune globulin, and further investigations have to be carried out immediately at the hospital. It is not uncommon for serum hepatitis B surface antigen and hepatitis B surface antibody to be positive at the same time in clinical testing. 1. Amino acid variations in the major hydrophilic region (MHR) of the S gene of hepatitis B virus. 2. Successive and overlapping infections with different subtypes of hepatitis B virus: re-infection with different subtypes is also one of the reasons for the coexistence of hepatitis B surface antigen and hepatitis B surface antibody, which can provide protective immunity against all subtypes of HBV infection, but the antibodies to other subtypes are not cross-protective. 3. Positive hepatitis B surface antigen and hepatitis B surface antibody can also be seen with the hepatitis B vaccine or hepatitis B immune globulin used for vaccination. If hepatitis B antigen and antibody are positive at the same time, go to the hospital immediately for further examination and treatment under the doctor’s guidance.