Although Southeast Asia is one of the last strongholds of endangered dholes (Cuon alpinus), or Asiatic wild dogs, little is known about dhole ecology in this region. We used scat collections, prey surveys, and camera-trap data to determine the diet, prey selection, and activity of dholes in a national protected area in northern Laos. Results showed that dhole diets were dominated by ungulates (87% of biomass consumed), with additional prey including other carnivores (6%) and rodents < 1 kg (6%). Concerning individual prey species, only muntjac (Muntiacus, 45%) and sambar (Rusa unicolor, 33%) contributed >7% of biomass consumed. Dholes were not random in their consumption of ungulates, because muntjac (20–28 kg) and sambar (185 kg) were selectively consumed over medium-sized (75- to 85-kg) ungulates. Dholes were almost exclusively diurnal, and their activity pattern was significantly different (all P < 0.003) from that of all ungulate species except wild pigs (Sus scrofa). Overall, prey selection by dholes appeared to be more influenced by social behavior and terrain use of ungulates, rather than by body size or activity of ungulates. In tropical forests of northern Laos, dholes focused predation on relatively few species during diurnal hours, suggesting the management of muntjac and sambar may be important for conserving dhole populations in the region.