Mitochondrial Cytochrome Oxidase Subunit I DNA sequences are a good discriminative marker for phylogenetic studies in crustaceans and especially in amphipoda. In the present study, molecular and morphological data were analyzed to test whether Gammarus lobifer authority and Gammarus balutchi authority which one or two geographically separated but morphologically similar species. The analyses proved that there are two species and that uplift of the Zagros Mountains was probably the most important cause of Allopatric speciation in this region during the Miocene period.