The determination of the synanthropic index is essential to evaluate the degree of association between species, such as diptera and man, based solely on their degree of preference for urban areas. This research aimed to study the synanthropic behavior of Calliphoridae and Mesembrinellidae flies in Rio de Janeiro, Brazil. The experiment was conducted between 2021 and 2022 in three areas, where four traps containing 300 g of fresh liver or with 48 h of putrefaction were installed, remaining exposed for 48 h; after collection the dipterans were sacrificed and taxonomically identified. A total of 2,826 dipterans were collected, represented by nine species of Calliphoridae (89.24%) and ten of Mesembrinellidae (10.76%), with the first record ofMesembrinella curraniin this biome. The Kruskal-Wallis test showed that the abundance of individuals did not differ among the three analyzed environments. The Mesembrinellidae family was exclusively asynanthrope, along with two species of Calliphoridae:Hemilucilia benoisti(Séguy 1925) andParalucilia nigrofacialis(Mello 1969) which were exclusive of the forest area, while Calliphoridae had varied synanthropy.Lucilia eximia(Wiedemann 1819) alone represented 57.18% of the total sampled, being the most abundant in all environments except the urban area whereHemilucilia segmentaria(Fabricius 1805) totaled 55.73%. No species were exclusive to the urban area, howeverCochliomyia hominivorax(Coquerel 1858) andLucilia cuprina(Wiedemann 1830) were exclusive to the rural area. The most synanthropic species wereChrysomya megacephala(Fabricius 1794) andChrysomya albiceps(Wiedemann 1819).