Xishuangbanna, lying between 99°56´ and 101°50´E longitude and 21°08´ and 22°36´ N latitude of southern Yunnan, is located on the northern fringe of the tropics. Its orchid flora is very rich but little known to the outside world. From 1980 to 1992, the authors tripped seven times to that region collecting and studying orchids there. As a result, 335 species and two varieties belonging to 96 genera were identified as indigenous to Xishuangbanna region. Among them, two genera (Pennilabium J. J. Sm. & Parapteroceras Averyanov), 50 species are new to China, 190 species new to this region, and 21 species and one variety are endemic to Xishuangbanna. It is interesting to note that both genera and species native to Xishuangbanna are more than those in Hainan and comparable to those in Taiwan, though the collection in this region is not complete.