Abstract: Based on sample plot investigation to Bombax ceiba forest in Monghan basin of Xishuangbanna, Yunnan, a report on the forest in detail is presented in the paper. The forest oc-curs along the Lancang River (upper Mekong) at the alluvial soft soil. With only one tree layer and a indentical physiognomy, as well as lower species riches, the forest is a secondary forest with single dominant tree species Bombax ceiba. It is concluded that the forest could form from gregation of Bombax ceiba at the alluvial soft soil and with collapse and reconstruction of the al-luvial soft riverstep old the forest falls apart and new one appears on new riverstep again.

Key words: Xishuangbanna