Klias Forest Reserve is a protected forest reserve on the Klias Peninsula, in Beaufort District of Interior Division, Sabah, Malaysia. It was designated as a Class 1 Protection Forest by the Sabah Forestry Department in 1984. Its area is 3,630 hectares (36.3 km2). The reserve is mostly flat, consisting mainly of peat swamp forest, with a small area of mangroves. The peat forests within this reserve, along with those in the nearby Binsuluk Forest Reserve, are the last peat forests in Sabah.