The feeding selection of leaves by chimpanzees was investigated from the perspective of phytochemistry and leaf availability. Field data were collected for 6 months from 1995 to 1996 and 8 months from 1997 to 1998 in Bossou, Guinea. Time budgets of leaf consumption by chimpanzees were analysed and the abundance of young leaves of each tree species for each month was estimated. Analyses of dried materials, stratified by leaf maturity and edibility, for the relative amounts of crude protein, crude fat, neutral detergent fiber, ash, and condensed tannin were determined. It was found that 1) leaves consumed by chimpanzees had higher levels of ash and lower levels of condensed tannin than leaves that were not eaten; 2) feeding selectivity was correlated with crude protein content; and 3) the availability of young leaves was not correlated with the percentage of feeding time, neither by seasonal changes nor by tree species. Chimpanzees preferred leaves containing higher protein content, but did not consume leaves containing high condensed tannin regardless of protein content. It seems reasonable to consider that a different rule exists for "whether chimpanzees eat it or not" and "whether they prefer it or not" in phytochemical determinants of leaves. Some Moraceae species, which had low levels of condensed tannins, even in mature leaves, were an important food source for the Bossou chimpanzees.