RESUMO: The increasing occurrence of drought worldwide underscores the need to understand how rainfall seasonality influences species abundance and temporal availability of the ecosystem functions they provide. Here, we evaluate the effects of rainfall seasonality on dung beetle assemblages (species richness, abundance, species composition, and biomass) and their ecological functions (dung removal and soil bioturbation) in introduced pastures within the Brazilian Cerrado. To achieve this, we sampled dung beetles and measured their ecological functions in 10 pastures during the dry and rainy seasons in Aquidauana, Mato Grosso do Sul, Brazil. Our results showed a decline in species richness, abundance, and biomass, along with reduced ecological functions from the rainy to the dry season. These findings indicate that rainfall seasonality affects not only dung beetle assemblages but also impacts the ecosystem services directly associated with these organisms. Furthermore, dung removal was positively correlated with species richness and biomass during the rainy season but not in the dry season. As dung beetles are essential for maintaining functional pastures, understanding their responses to seasonal variation is critical for predicting climate change impacts on these insects and their ability to provide key ecosystem services, such as nutrient cycling, parasite control, and soil fertility. Implications for insect conservation: We emphasize the importance of conservation strategies to mitigate the effects of increasing drought and ensure the maintenance of ecosystem services in tropical pasturelands. Finally, our findings contribute to a deeper understanding of the biodiversity–ecosystem function relationship under climate change.