Hemophilia A, known as one of the most common inherited bleeding disorders, is caused by FVIII gene mutations. Among serious Hemophilia A cases, inversion of intron 22 (inv22) is considered to be a popular one, originating 40 percent of them, and is the major factor for inhibitor development. Therefore, the inv22 plays highly important part in patients' prognostic. Long-range PCR has been commonly used for detecting this mutation so far. In National Institute of Hematology and Blood Transfusion, the authors have been doing research to apply this technique for detecting inversions inv22 for patients with severe Hemophilia A. This paper presents research results as well as provides preliminary results of the percentage of patients positive with inv22 in the group of patients studied.