A Ca.sup.2+ dependent recombinant antibody that specifically binds to a specific twelve peptide sequence (E D Q V D P R L I D G K) in the activation region of the Protein C has been constructed. The antibody does not bind to Activated Protein C and can be used to inhibit activation of Protein C by thrombin-thrombomodulin, in purification of Protein C, and in treatment of tumors.