We studied the diet composition and preference of giraffe in mosaic thicket. Diet composition was determined by direct observations throughout the year. The Jacobs index was used to calculate dietary preference indices. Although the recorded diet consisted of 20 browse species, 17 were tree/shrubs, and only two, Acacia karroo and the invasive alien Acacia cyclops, formed the bulk of the annual giraffe diet. On a seasonal basis, the deciduous A. karroo was the main food in spring/summer/autumn when it was preferred but it became less important in winter when it was not preferred. Although the evergreen A. cyclops was preferred by giraffe in all seasons, it became slightly more important as a forage source in winter when evergreen shrubs formed the bulk of the diet. Of the 17 shrub species recorded in the diet, only four were preferred by giraffe in spring/summer/autumn and seven in winter. A. karroo and other preferred species are therefore likely to be under pressure from heavy browsing in mosaic thicket, especially in situations when the alien A. cyclops is absent. We suggest that A. karroo and the palatable Grewia occidentalis could be used to prompt adjustments to giraffe stocking rates on wildlife ranches in mosaic thicket of the southern Cape.