Fire is a widely used tool to prepare deforested areas for agricultural use in Amazonia. Deforestation is currently concentrated in seasonal forest types along the arc of deforestation, where dry-season conditions facilitate burning of clear-felled vegetation. Interior Amazon forests, however, are less suitable for fire-driven deforestation due to more humid climate conditions. These forests will ultimately come under more intense pressure as the deforestation frontier advances. Whether these regions continue to be protected by humid conditions partly determines land use changes in interior Amazon forests. Here, we present a study of the climate constraint on deforestation fires in Amazonia under present-day and projected climate conditions. We used precipitation data and satellite-based active fire detections to model fire-driven deforestation potential. Our model results suggest that 58% of the Amazon forest is too wet to permit fire-driven deforestation under current average climate conditions. Under the IPCC B1 scenario, the model indicates increased fire potential by 2050 in eastern Amazonia, while dry-season precipitation may provide limitations on projected deforestation by 2050 in central and western Amazonia. However, the entire region is very sensitive to a possible drying with climate change; a reduction in dry-season precipitation of 200 mm/year would reduce the climate constraint on deforestation fires from 58% to only 24% of the forest. Our results suggest that dry-season climate conditions will continue to shape land use decisions in Amazonia through mid-century, and should therefore be included in deforestation projections for the region. Copyright 2010 by the American Geophysical Union.