Ust-Dunguy (; , Dunguin Adag) is a rural locality (a selo) in Kyakhtinsky District, Republic of Buryatia, Russia. The population was 712 as of 2010. There are 5 streets.
Ust-Dunguy is located 124 km southeast of Kyakhta (the district's administrative centre) by road. Anagustay is the nearest rural locality.