The study of the Upper Ordovician in the Faraghan Mountains, southeastern Iran, reveals for the first time the presence of a low-diversity trilobite fauna in the middle member of the Seyahou Formation. Five genera and nine species have been identified, including Dalmanitina (Dalmanitina) dargazensis nov. sp. Four species are described under open nomenclature and the affiliation of four taxa was possible only to the generic level. Overall, this trilobite assemblage shows strong affinities with high-to-mid latitude, peri-Gondwanan faunas, and displays close similarities with taxa from the Mediterranean margin of Gondwana (mainly Sardinia and Bohemia/Perunica) and, to a lesser extent, with the Turkish Taurides. The age of the Iranian trilobite fauna is well constrained, due to its co-occurrence with chitinozoans, which reveal a biostratigraphic interval ranging from the upper part of the Acanthochitina barbata to the Armoricochitina nigerica zones, mid-to-late Katian in age.