The UBSS expedition to northern Thailand during December and early January 2000/2001 investigated a previously unexplored area of karst near the northern border with Myanmar. A total of 2.5 km of cave passage was mapped in four adjacent areas and a large number of karst sites were investigated. The two largest caves were 718 m and 758 m in length. However, high levels of carbon dioxide in many of the caves proved a major hindrance to exploration. A description of the finds, coupled with a brief interpretation of the geology and geomorphology of the area is given below.