Two species of Diptera new for Switzerland (Syrphidae and Stratiomyidae) and complements to the list of Syrphidae of the canton of Geneva. – An ecological and faunistic study of the Moulin-de-Vert nature reserve (Cartigny, Geneva), carried out by Malaise trap from April to July 2019, revealed the presence of two species of Diptera new to Switzerland: Brachyopa obscura Thompson & Torp 1982 (Syrphidae) and Odontomyia annulata (Meigen, 1822) (Stratiomyidae). This study, together with other observations from the canton of Geneva, have added a total of nine new species to the list of Syrphidae in the canton and have confirmed the presence of 16 other species only known from historical records. A number of species recorded at Moulin-de-Vert, such as Criorina pachymera (Egger, 1858) and Mesembrius peregrinus (Loew, 1846), are only very rarely recorded in Switzerland. These results highlight the importance of this site, protected since 1970, and the fundamental role it plays in the conservation of biodiversity on both a cantonal and national scale