Invasive predators contributed to recent extinctions worldwide, including endemic birds. We monitored nests of two endemic birds in the Atlantic Forest, the serra antwren (Formicivora serrana littoralis) and the sooretama slaty antshrike (Thamnophilus ambiguus) during two consecutive breeding seasons, to estimate predation rates and identify the predators. As invasive marmosets apparently became locally common, we hypothesized that they would prey upon natural nests at a higher rate than native predators. We found 13 nests of the antwren and 15 of the antshrike, of which 100% and 73%, respectively, were preyed upon. Invasive marmosets preyed upon 13 of 16 nests (81%) with identified predators, affecting 90% and 67% of the antwren and the antshrike nests. This study documented that invasive primates negatively affect the breeding success of native birds in Brazil. We highlight the need for urgent measures to manage invasive marmosets to avoid the local extirpation of the endemic birds.