We studied sleeping sites used by chimpanzees in savanna woodland areas outside national parks in Tanzania from 1994 to 2011. We walked 1,043 km of census lines and recorded 479 beds in 193 clusters within 30 m from the census line. We prepared vegetation and topological maps using satellite and global information system data. We divided the census lines into square quadrates. A GLM showed that evergreen forests and slope affected the choice of sleeping sites. Chimpanzees made few beds in woodlands during the dry season simply because most woodland trees were defoliated. Bed distribution during the rainy season also showed that evergreen forests were included in more areas in the quadrates with beds than in the other quadrates with no beds. Chimpanzees might sleep in forests to reduce the predation risk by carnivores, because distances among trees was shorter and tree height higher than those in woodlands, and there was less grass in forests for carnivores to hide and hunt. Chimpanzees might sleep in hilly areas, because water is close to the bottom of the slope, and the carnivores might have difficulty chasing chimpanzees up the slope.