A study on on diversity of the family Orchidaceae at Bo Nam Sap and Kaeng Sam Phan Pi Nature Trial in Phu Chong Na Yoi National Park, Ubon Ratchathani Province was conducted from June to December 2007. There were 18 genera and 24 species. One of them is endermic to Thailand (Bulbophyllum orientale Seidenf.) And another is rare specie (Pecteilis susannae (L.) Raf.)