The survey of species diversity of the Cyperaceae along the nature trails in Nam Nao National Park covers 19 kilometers. It was divided into five trails, namely (1) The entrance gate to the tent areas (1.8 kilometers), (2) The short-nature trail (1 kilometers from Visitor Center), (3) Visitor Center via Dong Ma Fai to Tung Na Noi (3 kilometers), (4) The short-way to scenic view point (4.5 kilometers), and (5) The long-way to scenic view point (5.8 kilometers) (Figure 1). The collections of specimens were made every 2 weeks between November 2007 and November 2008. The plant collections were kept in the Khon Kaen University Herbarium (KKU) and the Forest Herbarium (BKF). The identification was made following Simpson and Koyama (1998). The local names are given following Simpson and Koyama (1998) and Royal Forest Department of Thailand (2001). Key to genera in the area is provided. Key to species is available from the first author.