Puspitaningtyas DM. 2018. Orchid exploration in Mount Bintan Besar Protected Forest, Bintan Island, Riau IslandsProvince, Sumatra, Indonesia. Biodiversitas 19: 1081-1088. Sumatra is one of the main islands in Indonesia. The biodiversity is higherthan Java, but still below compare to Borneo and New Guinea. About 1,118 species of orchids are found growing in Sumatra, which41% of these are endemic to Sumatra. The exploration activities were conducted at Gunung Bintan Besar Protected Forest, Bintanisland-Sumatra. Orchid exploration was conducted in this area to collect living plants for ex situ conservation purpose. Orchid inventoryto record orchid diversity in this area, based on plant collection by purposive random sampling. The results of the study recordedapproximately 23 orchid collection numbers found in that area. These were representative of 15 genera and consist of 14 species ofepiphyte orchids and 9 species of terrestrial orchids. Most orchids found in this area are lowland orchid which are very common inSumatra. Dendrobium metachilinum Rchb.f., Dendrobium leonis (Lindl.) Rchb.f. and Plocoglottis lowii Rchb.f. are unique orchidsspecies found on this island.