Keo Seima Wildlife Sanctuary (KSWS) is of national, regional, and global importance for a large number of species from a range of taxa. Here, we report on one component of the KSWS biological monitoring program—an updated KSWS species list. This list is the result of collaborative efforts among the Royal Government of Cambodia (RGC), non-governmental organizations (NGOs), visiting researchers from institutions across the world, national and international students, and citizen science initiatives. This list shows that, to date, 959 species have been recorded to occur within the boundaries of KSWS, the highest number published for any protected area in Cambodia.