Seasonally dry tropical forests are among the most vulnerable ecosystems to the effects of anthropogenic disturbances, and yet their biodiversity is still poorly known. In this study we investigated the composition, activity, structure, and effect of seasonality in mosquitoes’ assemblages of a conservation Caatinga domain unit. The collections consisted of the monthly installation of two Shannon traps, set at a distance of 8 km between them, and operated by two captors, who collected simultaneously for 3 h (17:00h to 20:00h), totaling 288 h of sampling over two years. In total, 1261 specimens belonging to at least 20 sp. of the subfamilies Anophelinae and Culicinae were captured. Culicinae was the most representative subfamily, with 99.3% of all collected specimens, while for Anophelinae only nine specimens of the species Anopheles albitarsis Lynch Arribálzaga, 1878 s.l. were registered. Among the species of Culicinae, Aedes scapularis was the most abundant (39.9%), followed by Mansonia wilsoni (21.6%), Culex spp. (12.8%) and Aedes taeniorhynchus (12.4%). The Culicidae assemblage was more abundant and diverse in the wettest months and the twilight hours (17:00h to 18:00h). Our data indicate that Anopheles species are sensitive to Caatinga arid conditions and that mosquito populations are controlled by rainfall.