Phlebotomus caucasicus Marzinovsky and Phlebotomus mongolensis Sinton are morphologically similar sand fly species. Finding a reliable, fast, and simple method to differentiate these two sand flies is important in understanding their role in the transmission of Leishmania parasite. In our study, 20 specimens of male P. caucasicus, 4 specimens of male P. mongolensis, and 16 specimens of female of both species (Caucasicus group) were examined by polymerase chain reaction (PCR). The result shows identical patterns with a visible fragment of about 500 bp in size. In restriction fragment length polymorphism (RFLP), we observed identical patterns with TasI used as the restriction enzyme. After alignment with sequences of the ITS2 partial gene in GenBank, a perfect match was obtained for the P. mongolensis, but not for P. caucasicus whose sequence was not present in the GenBank. Based on the results of our study, the RFLP-PCR method with nucleotide gene fragment ITS2 was a rapid and reliable method for differentiating these sand fly species.