ABSTRACT. Biology of Tolmomyias flaviventris (Wied, 1831) (Passeriformes, Tyrannidae) in the Atlantic Forest, Pernambuco, Brasil . Tolmomyias flaviventris is a wide species distributed in Pernambuco and well represented in the vegetation types found in Tapacura Ecological Reserve. The aim of this research was to study the biology of Tolmomyias flaviventris. The study was conducted in the Ecological Reserve of Tapacura, located in Sao Lourenco da Mata, Pernambuco State, between September 2001 and August 2002. To capture the birds, nine mist-nests were used and distributed equally among three different environments: edge and interior of forest and open field, collecting the following variables from birds: weight, molt, brood patch, measurements of wing, tail, tarsus, culmen and nostil of birds, besides capture time and date. The quantitative analysis data were collected by audio and visual information obtained in three different trails. Nest observation was also performed. Concerning the captures, 30 animals were mist-nested and measured, obtaining significant difference just between the weights of those captured in interior of forest and the animals from edge of forest. The open field was the environment which had the highest abundance of T. flaviventris. Amongst the birds captured, the most frequent brood patch was the number four. Concerning the quantitative analysis, 164 individuals were recorded. KEY WORDS. Atlantic Forest, Pernambuco, Tolmomyias flaviventris. RESUMO. Tolmomyias flaviventris e uma especie de ampla distribuicao em Pernambuco e nas diferentes formacoes vegetais da Estacao Ecologica do Tapacura. O objetivo deste trabalho foi estudar a biologia de T. flaviventris na Estacao Ecologica do Tapacura, Municipio de Sao Lourenco da Mata, Pernambuco. As capturas e observacoes foram realizadas entre setembro de 2001 e agosto de 2002, utilizando-se nove redes ornitologicas, tres em cada ambiente (borda, capoeira e interior mata). Dos individuos capturados foram tomadas as seguintes variaveis: massa corporea, muda, placa de incubacao, comprimento de asa, cauda, tarso, culmen e narina, data e hora de coleta. Para a analise quantitativa foram realizadas caminhadas em tres trilhas diferentes para a visualizacao e escuta da especie. Tambem foram realizadas observacoes dos ninhos de T. flaviventris e da placa de incubacao, sendo a mais frequente a de numero quatro. Entre as variaveis analisadas, apenas a massa entre as aves capturadas (n=30) no interior de mata e borda foram significativamente diferentes. A capoeira foi o ambiente que apresentou as maiores abundâncias. No levantamento quantitativo foram registrados 164 individuos nas tres trilhas. PALAVRAS-CHAVE. Mata Atlântica, Pernambuco, Tolmomyias flaviventris.