Hepatitis B core antibody (HBcAb) is a neutralizing antibody produced by the body’s immune system against the hepatitis B core antigen, and its positivity can represent patients who are infected with hepatitis B virus or who have recovered from hepatitis B virus infection. The intact hepatitis B virus is spherical in shape and consists of an envelope and a nucleocapsid. The nucleocapsid contains the core protein (HBcAg) and the ring-shaped double-stranded HBV-DNA, which is the center of hepatitis B virus genome replication. In response to the biological characteristics of the hepatitis B virus and the human immune response clinicians have developed a series of serological indicators for the detection of viral infection – hepatitis B five (commonly known as hepatitis B two and a half), hepatitis B core antibody (HBcAb) is one of them. Because core antigen exists in the nucleus of infected hepatocytes and is not easily detected in the blood, the only serologic marker for clinical detection of hepatitis B virus infection is hepatitis B core antibody, which becomes the “half-pair” of the hepatitis B two-and-a-half. The core antibody IgG can be detected in the serum of people who have been infected or are infected with the hepatitis B virus, and a positive core antibody IgM indicates a recent infection or viral replication of the hepatitis B virus. It should be noted that the disease state of hepatitis B infection is complex and varied, and clinical analysis should be combined with the five hepatitis B tests, hepatitis B virus DNA test and liver ultrasound or biopsy to correctly determine the condition of hepatitis B virus infection, which can be used to guide clinical treatment. In summary, HBcAb is one of the five indices of hepatitis B. Its positivity can represent patients who are infected with hepatitis B virus or have been infected with hepatitis B virus to recover, and should be combined with other related examinations and laboratory tests for comprehensive assessment of the disease and guidance of treatment.