Mayflies, order Ephemeroptera compose one of the main habitants of all the aqua systems around the world, which has valuable roles in several food chains. In this study, species diversity of Ephemeroptera in Jajrood River (Hajiabad, Saeidabad, and Khojir areas), eastern Tehran Province, was studied through spring-summer, 2016. Samples collected weekly and kept in Ethanol 80% for taxonomic identification. One hundred forty-nine samples belonged to 17 species, under 7 genera in 4 families (Baetidae, Heptageniidae, Habrophlebidae, and Isonychiidae) were collected. The majority of species abundance (45.63%) obtained from Khojir, although Hajiabad with 11 different species showed a more diverse collection for Ephemeroptera. Among the collected species, Heptagenia lateralis, Isonychia shima, Habrophlebia lauta, Labiobaetis atrebalinus, Labiobaetis potamoticus, Labiobaetis glaucus, and Baetis atlanticus were reported for the first time for Iran fauna and Baetis fauscatus andBaetisrhodaniwere the most common species. According to diversity indices, Khojir area along the River showed higher species collection. Knowledge of the species diversity in aqua systems in urban areas like Jajrood River would lead to new insight into ecosystem preservation and better management decisions.