We investigated dietary partitioning among tiger Panthera tigris, leopard Panthera pardus and dhole Cuon alpinus in Mudumalai Tiger Reserve, India between January 2008 and April 2010 based on scat analyses and prey surveys. Scat analysis revealed that though the diet of the three predators consisted of 15 to 21 prey species, wild ungulates formed a major portion of their diet (88.4 to 96.7%). The three predators exhibited high diet overlap (> 61%). Prey availability, estimated from an effort of 473 km of line transects (n = 33) revealed high density of chital Axis axis (43.8 ± 10.7 (mean ± SE) individuals/km²), followed by langur Semnopithecus entellus (31.0 ± 3.8), gaur Bos gaurus (6.7 ± 1.5), giant squirrel Ratufa indica (6.4 ± 1.3), sambar Rusa unicolor (4.9 ± 0.96) and elephant Elephas maximus (4.9 ± 0.75). Mean biomass (kg/km²) of chital, gaur and sambar was 2058.6, 3015 and 656.6 respectively. In terms of biomass, tiger consumed mostly large sized prey (> 50 kg). Although leopard and dhole selected mostly medium-sized (11–50 kg) prey (chital), the second most important prey was sambar for dhole and langur for leopard. The results suggest that high density of different-sized prey in Mudumalai Tiger Reserve helped facilitate coexistence of tiger, leopard and dhole, despite the high dietary overlap, although some dietary partitioning was apparent when considering prey size and prey selection.