Food and feeding behaviour of the introduced Formosan squirrel (Callosciurus sp.) were studied in Nogeyama Zoo, Yokohama City, Kanagawa Prefecture, Japan, from August 1981 to July 1982. Throughout the field observations, various parts of 29 species of trees and one species of fungus were used as food. The main food trees wereCastanopsis cuspidate, Prunus (Cerasus) spp., Morus austraris, andAcer palmatum. Various parts of these food trees were eaten depending on season : mainly fruits and cones in autumn, bark and bubs in winter, bark and flowers in spring, and fruits and cones in summer. The cumulative frequency of feeding per tree over a year was high on the tree species which produced mainly fruits or cones. It should be noted that the squirrels changed their feeding behaviour depending on the kinds of food. Adaptability to the wide range of foods and ability to change the food habit are thought to be the factors which made this species possible to settle outside their native habitats.