The present invention provides a method for improving or controlling the plasma half-life and/or bio-availability of blood coagulation factor IX (FIX), the method comprising modifying the GLA domain. Examples of such modifications include: (i) non-covalent bonding of a GLA-domain-recognizing antibody or an antibody fragment thereof to the GLA domain； (ii) reduced number of Gla residues in the GLA domain, in comparison to that of a native FIX； (iii) either or both of deletion of one or more glutamic acid residues in the GLA domain and substitution of one or more glutamic acid residues in the GLA domain with another amino acid； and (iv) deletion of a part or all of the GLA domain. The present invention also provides a FIX with improved pharmacokinetics which carries such modifications, a pharmaceutical composition containing the FIX as an active ingredient, a method for producing the FIX, and such.
