The temperature and habitat gradients of tropical mountains contribute to their high species diversity and endemism. Recent fieldwork in the Central Highlands of Vietnam has found many taxa new to science, but the area remains poorly explored. We surveyed the butterflies of Kon Ka Kinh National Park between 1999 to 2019 and noted the habitat, seasons, and freshwater availability for each transect in 2018–2019. We found a total of 368 butterfly species including 80 documented in that region for the first time in 2018–2019. Nymphalidae (41.8%) was the most abundant butterfly family, and Riodinidae was the least common. We recorded higher species richness in disturbed forests, but many of the species we document are endemic or have restricted ranges. The diverse fauna is at a biogeographic crossroads of mostly Indo-Malayan species from the south and some high elevation specialists from the north meeting along an elevational and climatic gradient. Correspondence analysis demonstrates that season and forest type are the most important environment covariates influencing butterfly abundance in this unique tropical forest. These results demonstrate that the Central Highlands of Vietnam are not only species rich, but also home to many rare and endemic species found nowhere else, making the area a conservation priority.