Cheetahs Acinonyx jubatus are important predators of herbivores in African ecosystems, and several methods to determine their diet have been used in the past. We applied a novel method to quickly assess the diet of cheetahs with respect to grazing and browsing herbivores, i.e. we analysed the stable carbon isotope ratio (δ13CV-PDB) of cheetah breath to separate individuals feeding predominantly on browsers or grazers, respectively. Browsers and grazers are contrasting in their muscle δ13CV-PDB, because of their isotopically distinct C3 or C4 plant diet, respectively. Muscle δ13CV-PDB of six abundant local potential prey species of cheetahs confirmed that kudu Tragelaphus strepsiceros and springbok Antidorcas marsupialis browsed on C3 plants, whereas gemsbok Oryx gazella, hartebeest Alcelaphus buselaphus, warthog Phacochoerus africanus and cattle Bos taurus predominantly grazed on C4 plants. Breath δ13CV-PDB of the cheetahs followed the bimodal frequency distribution of the prey species with six cheetahs being assigned to the C4 food web and three to the C3 food web. Breath tests may be a suitable method to delineate the trophic membership of carnivores to C3 and C4 food webs when animals are chemically immobilised for other purposes.