Kloss gibbons are the same size and live in the same type of habitat as several other gibbon species, and consequently its diet would be expected to be similar to its closely related congeners. The diet is described in terms of the weight of food items, faecal remains, and time devoted to different foods. Aspects of feeding behaviour are then examined, such as changes in food choice through the day, the relationship between fruit size to feeding bouts and feeding rates, and the effect of forest type quality on ranging. A comparison is made between gibbon species. The diet of Kloss gibbons appears to differ from that of other gibbons in that it contained no tree leaves, and arthropods were a major part of the diet. Possible reasons for this are discussed.