The MBZ funds has been key for our NGO, Three monkeys Wildlife Conservancy, towards the rediscovery of a remnant population of the critically endangered Delacour’s langur (Trachypithecus delacouri) in the Yen Mo Limestone Complex, significantly enhancing our understanding of the species’ distribution and conservation status. Through a combination of interview surveys, ground surveys, and drone surveys, 37 individuals across four groups were documented, primarily confined within the Yen Mo District Forest. This discovery marks the third-largest population of the species. In addition, the survey also provided comprehensive insights into other wildlife, revealing diverse species, including two macaque species (Macaca mulatta and Macaca assamensis), the Indochinese serow (Capricornis maritimus) and the Keeled Box Turtle (Cuora mouhotii), some of which are listed by IUCN as vulnerable and CITES-listed. However, persistent threats such as hunting activities, although no direct evidence on langurs, along with other anthropogenic activities such as agriculture and quarrying, underscore the urgent need for conservation action. The current fragmented management of the area poses significant challenges, necessitating a unified management approach that transcends administrative boundaries. Establishing a management board, strengthening enforcement measures, and upgrading the protection status of the area are crucial steps toward safeguarding Delacour's langur. This species, in turn, has the full potential to serve as a flagship species for the entire limestone complex, drawing attention to its conservation needs and highlighting the importance of preserving its broader ecosystem.