In the west part of Tokyo, the giant frying squirrels (Petaurista leucogenys) eat the leaves of the deciduous tree Quercus acutissima from spring to summer. They eat the central part of the leaves. In winter, when there is no Q. acutissima leave, the leaves of the evergreen tree Q. sessilifolia are used as food by them. Sometimes they eat the central part of the leaves as in Q. acutissima. Then we measured the distasteful phenol concentration and distribution within the single leaf of these two trees, and examined the phenolic contents affect seasonal feeding behavior of the squirrels. As a result, in Q. acutissima, avoidance of the peripheral parts of the single leaf was explained by the higher total phenolic contents than the central parts. Q. sessilifolia leaves have lower contents of phenols than Q. acutissima leaves during the year, and the phenol is distributed homogeneously within the single leaf. However, the squirrels often eat Q. sessilifolia leaves in the same feeding manner as in the Q. acutissima. Because Q. acutissima leaves are preferable food for the squirrels and they may follow this feeding manner for other temporally used food such as Q. sessilifolia leaves.