The robber flies (Diptera: Asilidae) were studied in northwestern Iran. Specimens were collected using sweeping net and Malaise traps during 2010–2019. A total of 27 species were collected and identified, of which five species are recorded for the first time from Iran: Aneomochtherus mundus urartorum (Richter, 1960), Dysmachus cochleatus (Loew, 1854), Erax hayati Tomasovic, 2002, Leptogaster stackelbergi Lehr, 1963, and Stenopogon porcus Loew, 1871. A new species, Crobilocerus flavus Sakhvon & Mohammadi sp. n., is described and illustrated. Nine species are recorded from northwestern Iran for the first time. A key to males of Crobilocerus is provided. An updated list of 309 species and subspecies belonging to ten subfamilies of the robber flies from Iran is provided. [ABSTRACT FROM AUTHOR]