Resumo. Social wasps are commonly considered generalists in their feeding habits, but there are genera with little information regarding their diet, such as Mischocyttarus de Saussure, 1853 (Hymenoptera: Vespidae), the most species-rich wasp genus in the world. The objective of this study is to report Mischocyttarus rotundicollis (Cameron, 1912) (Hymenoptera: Vespidae) feeding on a spider in the southeastern region of Brazil, aiming to expand information about its feeding behavior. The record occurred occasionally on September 23, 2023, in the state of Minas Gerais, Brazil, in the ecotone region between the Atlantic Forest and the Cerrado. The feeding of a species from the Araneidae family occurred in its web, and the individual of M. rotundicollis used the tarsi of its legs to cling to the silk threads of the web, which could suggest a specialization for the exploitation of this food resource. Our record provides further information on the feeding behavior and diet of M. rotundicollis and presents the first information on spider feeding by this species. Further studies are suggested to evaluate this possible hypothesis of specialization of the genus for foraging in spider webs.