Abstract: Hemophilia B is an X-linked bleeding disease, caused by the mutations of human coagulation factor IX (hFIX) gene located in chromosome X. It results in a dramatic decline of hFIX quantity or clotting activity in plasma, and the intrinsic clotting pathway is affected seriously. In this article, the structure and function of hFIX gene as well as the protein encoded by this gene were reviewed. Various types of hFIX mutants found in hemophilia B were also described, including the mutations caused by founder effects, mutations in regulatory region, coding region, splicing sites of introns and two other special mutations. Meanwhile, the biological effects of the mutations described above were discussed. Finally, a mutation type (Arg→Ala at point 338) that can increase the clotting activity of hFIX as well as the potential application was briefly introduced.