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Background and Objective: Visceral Leishmaniasis or Kala-azar is an important infectious disease in northwestern Iran. Members of the Leishmania donovani complex, L. donovani and L.infantum, are the two main parasites causing the disease in the world. In this study immunophenotype characters such as N-glycosylation, and T-cell and B-Cell epitopes of CPB gene was evaluated in the Leishmania parasites isolated from sandflies of the region. Materials and Methods: Partial of the CPB (702-741 bp) of Leishmania parasites was amplified and sequenced and used for bioinformatics analysis such as test three dimensional (3D) protein structure, N-glycosylation, and T-cell and B-Cell epitopes. Results: In 7 out of 3477 sand flies there was a positive PCR test for systeine protease B, gene. Also according to findings of this study, both agents of kala-azar L. donovani and L. infantum were bing transfered by sand flies of Phlbtomus perfiliewi transcaucasicus in North West Iran. DNA analysis of the CPB gene showed a cytosine insertion at 5’ end of the proofreading frame of the gene resulted in a stop codon (TGA) seven AA further down and hence translation is halted. This caused a short amino acid chain with only 76 AA much shorter than normal CPB peptide with 234-247 AA. This mutation has not been found in the L.infantum strain resulted in a normal CPB peptide. AA analysis showed no N-glycosylation site, T-cell and B-Cell epitopes on the short peptide of the L. donovani strain. Conclusion: This is the shortest CPB peptide chain reported for the L. donovani complex in the literature. This short peptide could have an effect on host-parasite and vector-parasite interactions. Since the CPBs genes have important implication on host–parasite and play key roles in infection and expression of the disease, further studies on the L. donovani parasite and its diminutive peptide necessitate to improve our understanding about the epidemiology of visceral leishmaniasis in Iran.