Keo Seima Wildlife Sanctuary (Khmer: ដែនជម្រកសត្វព្រៃកែវសីមា) is a 2,926.9 km2 (1,130.1 sq mi) protected area of mixed seasonal tropical forest in eastern Cambodia, located in Mondulkiri and Kratié provinces.

[1] The site is of national, regional, and global importance for a range of biodiversity, with more than 950 species recorded within the protected area.

[2] Keo Seima Wildlife Sanctuary (KSWS) lies between 60 and 750 metres (200 and 2,460 ft) above sea level, and is situated in the southeast corner of Cambodia along the border with Vietnam.

Mixed forest types and a range of elevation gives rise to a rich collection of biodiversity, both flora and fauna.

[2][9] Seven primate species are found in the protected area, including the vast majority of the world's population of the black-shanked douc langur, with an estimated 25,000 individuals.

KSWS is also covered parts of two Important Bird Areas: KH026 (the Mondulkiri - Kratie Lowlands)[19] and KH027 (Snoul / Keo Sema / O Reang).

[28] These titles have already proved vital for communities, allowing them to resist illegal land grabs,[29] with one precedent-setting case reaching the high courts.

[39] The majority of KSWS is included in a REDD+ project that is the largest carbon emission reduction program in Cambodia's land use sector.

[40] The project was the first initiative in Cambodia to use an extensive free, prior and informed consent process with independent legal advice,[43] and local communities from 20 villages in and around the protected area have signed agreements to join the KSWS REDD+ project and receive a proportion of profits from the sale of carbon credits.

[47][48] KSWS shares its eastern border with Vietnam, and cross-border trade contributes to illegal logging of high value timber species.