<p>Biodiversity in Southeast Asia is currently facing a significant decline, with primate species particularly impacted due to deforestation, poaching, global warming, and various other challenges. All 20 recognized gibbon species are considered at risk of extinction due to rapidly decreasing population sizes. The northern white-cheeked gibbon (<i>Nomascus leucogenys</i>) is among six gibbon species belonging to the genus <i>Nomascus</i> documented in Vietnam. This gibbon has been recorded in several protected areas, but significant populations persist only in a few locations, potentially including Vu Quang National Park (52.733 km²). In our study, we utilized the auditory point count method to collect data in the field and applied a distance sampling method to estimate the abundance of northern white-cheeked gibbons in Vu Quang National Park. A total of 27 gibbon groups were documented during our field survey. The estimated gibbon group density was approximately 0.48 groups/km², leading us to estimate the gibbon population size in Vu Quang National Park at about 155 groups. Vu Quang National Park therefore has the largest documented population of northern white-cheeked gibbons in Vietnam, highlighting the urgent need for prioritizing the conservation of this species.</p>