polystictus superciliaris (wied, 1831) is a small tyrant-flycatcher endemic to mountaintops in the highlands of eastern brazil. in this paper we present the first description of the breeding biology of p. superciliaris and estimate its reproductive success from a population inhabiting rocky outcrops. this study was conducted during 2005 in the parque estadual da serra do rola mo？a, municipality of nova lima (20°03's, 44°00'w), state of minas gerais, southeastern brazil. fourteen pairs of p. superciliaris were banded and monitored. the onset of the breeding season in 2005 was assumed to have been sometime before the 26th of july, while it was assumed to have ended on the 23rd of november based on the last observation of a successful brood. clutch size was invariably two eggs (n = 21), the incubation period averaged 17.7 ± 1.3 days (n = 9), and the nestling period averaged 16.4 ± 1.3 days (n = 8). we estimated the probability of reproductive success for p. superciliaris to be 41.3%, during this particular breeding season. of the 12 (57.1%) unsuccessful nests, eight (66.7%) had eggs and four (33.3%) had nestlings when they failed. in nine (42.8%) of these cases, the nests were lost to predation, two to parasitism by botflies, and one due to abandonment. this study suggests that the reproductive success of p. superciliaris is intermediate compared to the other species of tyrannidae that have been studied and closer to the lower limit of the 40%-80% range which is characteristic of tyrant _ flycatcher species that breed in temperate regions.