The Fulvous-breasted Flatbill (Rhynchocyclus fulvipectus) has an Andean distribution from Colombia and Venezuela to northeastern Bolivia between 750 and 2,300 m elevation. We describe the nesting behavior, nest, eggs, and nestlings of this species in the buffer zone of Manu National Park at Cock of the Rock Field Station, Cusco, Peru, from August through December 2009. We monitored seven nests using data loggers to describe incubation patterns and conducted direct observations of provisioning behavior. The two-egg clutch size and pear-shaped nest structure were consistent with previous reports. Incubation lasted 24 days (n  =  1) and nestlings were in the nest for at least 29 days. We only observed one parent incubating (presumably the female) with average nest attentiveness of 64%, which decreased as the incubation period progressed. The adult made 10 to 15 foraging trips per day (n  =  21) during incubation, when it spent on average (±SD) 32.9 ± 2.8 min during incubation bouts and 23.1 ± 6.3 min during foraging bouts (n  =  3 nests). Nestlings were able to regulate their body temperature after the feathers were fully developed; however, their body temperature (37° C) was lower compared to adults. We confirmed Rhynchocyclus nests exclusively along creeks or rivers and also revealed long incubation and nestling periods, which may be more common than expected in tropical mountain areas. There was a decrease in nest attentiveness through time, contradicting previous findings on neotropical passerine species.