A new subspecies of freshwater amphipod, Gammarus komareki aznavensis subsp. nov., collected from Aznav County (Khalkhal-Ardabil), northwestern Iran, is described and illustrated. The new subspecies belongs to the Gammarus pulex-group and has characteristic features similar to Gammarus komareki. Shorter flagellum of antenna 1, kidney-shaped and bigger eyes, more setose outer margin of the exopodite of uropod 3, and shorter endopodite of uropod 3 are the most obvious features that differ from G. komareki. A detailed morphological description and illustrations of the new subspecies are given and differences from related species are discussed.