Abstract: Ethnobotany is a newly developed comprehensive plant science, which mainly focuses on the direct interrelation between human beings and plants. Ethnobotany has only been established since 1982. However it has achieved marvelous development and fruitful results during the past two decades. The development of national medicine is one of important content of ethnobotany, and the Li nationality in Hainan province has possessed a lot of knowledge and experience in the usage of plants. In this paper, the conception and developing progress of ethnobotany were introduced. Based on the brief discussion of relation between the traditional medicine and plant resource exploitation by the Li nationality, the current situation on medicinal plant resource exploitation in Hainan island has been generalized and some suggestions has been proposed.