To study the functions of pre-pro leader peptides of the human and porcine prothrombins on the human FIX (hFIX) expression. In silico analysis predicted higher secretion efficiencies for the prothrombins-derived signal peptides, in comparison with the native hFIX signal peptide. Replacements of the hFIX pre-pro sequence with those of the two prothrombins, led to increased levels of transcription of the chimeric transgenes, as compared to the native clone. This was in consistent with the lower minimum free energies, calculated for the recombinant transcripts, based on their secondary structures. Evaluation of secretion efficiency revealed that the highest and lowest FIX secretions belong to signal peptides derived from porcine' prothrombin and hFIX, respectively. Coagulation activities of the FIX expressed from chimeric variants could be increased up to tenfold, relative to the native clone. The feasibility of a leader-peptide replacement for the improvement of both transcription and post-transcriptional processes is described that can be relevant for production the vitamin-K dependent proteins.