Abstract: Disclosed is an expression vector system for variants of coagulation factor VIII (FVIII) and von Willebrand factor (vWF). In detail, mutant vWF the size of which is significantly reduced by deleting exons but which has remarkably increased FVIII stabilizing and activating efficiency, and an expression vector system useful for the treatment of hemophilia which is capable of expressing the same along with FVIII are disclosed. Use of the mutant vWF with a reduced size enables effective expression of FVIII in a viral vector and significantly enhanced FVIII activity. Further, the viral vector may be effectively used to treat hemophilia through gene therapy.