IgG is the main immunoglobulin, brings the immunolgic effects in body. The human IgG can be divided into four kinds; IgG1, IgG2, IgG3, IgG4, respectively. The structures of IgG1, IgG2, IgG3, IgG4 are different, therefore, their functions are also different. The defects, increase or imbalance of the IgG subtypes in autoimmune diseases, infectious diseases, cancer and other diseases are indicators of the immune response. IgG1, IgG2, IgG3 and IgG4 also play a different important roles in the disease progress. The analysis of IgG subtypes is beneficial to study the etiology, pathogenesis and prognosis of above menthioned deseases. This review briefly summarizes the characteristics of IgG subtypes in thrombotic thrombocytopenic purpura, autoimmune hemolytic anemia, hemophilia, lymphoma and leukemia.