Littoral diatoms were studied in two locations in the Shatt Al-Arab estuary, North West Arabian Gulf, a eutrophic brackish to marine environment whose diatom flora appears to be poorly known. A total of 170 taxa belonging to 70 genera were identified and documented by light microscopy. Large numbers of freshwater taxa washed down from the inland waters of South Iraq were observed. Cocconeis placentula and its variety euglypta, Cyclotella meneghiniana, Cymbella aspera, Gomphonema coronatum, G. truncatum, Pinnularia divergens and Surirella capronii were the most common freshwater taxa. The majority of the recorded taxa have a cosmopolitan geographic distribution, but some tropical and subtropical ones were also common: Cyclotella stylorum, Tryblioptychus cocconeiformis, Trachyneis debyi, Trachyneis antillarum, Trachyneis spp. and Gomphotheca sinensis. The taxon Navicula lyra var. abnormis Grunow in A. Schmidt is recombined in the genus Lyrella Karajeva and at the same time its taxonomic rank is raised to that of a species, Lyrella abnormis (Grunow in A . Schmidt) comb. et stat. nov. Navicula peculiaris Salah et Tamas is proposed as a taxonomic synonym of Lyrella abnormis.