Saddleback toads (Brachycephalidae: Brachycephalus) are a remarkable group of highly endemic species from the southern Atlantic Rainforest of Brazil. They are brightly colored, diurnal, minute frogs that live in the leaf litter of high-elevation cloud forests. Little is known about the natural history of these frogs, particularly their diet. In the present study we provide the first published account of a Brachycephalus species diet. Specimens of Brachycephalus brunneus Ribeiro, Alves, Haddad & Reis, 2005 (N = 20) were collected from two locations in the Serra do Mar mountain range in the state of Paraná, southern Brazil. A total of 137 food items were recorded, with Acari being the most common item (62.4%). This prevalence is much higher than the actual availability of Acari in their environments (37.7% of all items in leaf litter samples) and therefore indicate their preference for this food item.