Leaf traits can limit or promote flammability, but how these traits vary and influence forest flammability in humid tropical forests is unknown. Species within the south-eastern transitional forests of the Brazilian Amazon are experiencing fire, particularly surface fires, with greater frequency and severity than historically recorded. In this study, the leaf traits and consequent burning characteristics of the 17 most abundant species in a transitional forest in Mato Grosso, Brazil were analysed through controlled combustion experiments and leaf trait measurements. Mean maximum flame height (range 52–108?cm), flaming duration (range 21–71?s) and mass loss (range 82–97%), which relate to a fuel’s combustibility and consumability, varied substantially across species. Measured leaf traits, mainly surface area and volume, accounted for 78% of this variability. The most flammable species were those with thin, lightweight and loosely packed leaves, which produced rapid, intense fires that consumed larger fuel amounts. The least flammable species had thick, large and densely packed leaves. In diverse tropical forests, analysing the relationship between species-specific leaf traits and flammability will yield insights into fire behaviour and future forest composition in a frontier zone where exposure to anthropogenic fire is high.