The recently discovered coagulation factor Ⅸ/factor Ⅹ-binding protein family is widely present in the venom of viperidae snake, which is an unique subfamily in the C-type animal lectin superfamily. The proteins of this family are non-enzymatic anticoagulants that bind to the Gla-domain regions of factor Ⅸ or factor Ⅹ and form 1∶1 complexes with factor Ⅸ or factor Ⅹ in the presence of Ca²⁺ ions. They are heterodimeric proteins consisting of two highly homologous peptide chains linked by a single disulfide bridge. Each chain contains one Ca²⁺-binding site and an intrachain disulfide-bonding pattern similar to those of C-type carbohydrate recognition domain. The amino acid sequences of this family exhibit high homology amid them. The crystal structure of habu coagulation factors Ⅸ/Ⅹ-binding protein has been determined. It is an intertwined dimer with a central loop projecting into the adjoining chain. Excluding this loop, each chain has a fold similar to rat mannose-binding protein.