Abstract: Jianfengling Nature Reserve has been enlarged from 7,762 hm² to 20,170 hm² since it was approved as a national nature reserve in 2002. For planning conservation strategies, Hainan University carried out fieldwork to investigate plant species diversity of the enlarged area in October 2003. Forty-three species were recorded for the first time in the Jianfengling region, including five species endemic to Hainan Island, namely Aristolochia fulvicoma, Stephania hainanensis, Tutcheria ovalifolia, Melicope patulinervia, and Lyonia ovalifolia. In 9,600-m² standard plots of natural forests established in this investigation, 398 species including 3,466 standing trees with height≥1.5 m were recorded, belonging to 161 genera and 69 families. In this area, 41 species were in the list of national endangered and protected plants, and their vertical distribution was described. Among them, Antirhea chinensis and Chuniophoenix hainanensis were newly recorded in Jianfengling forests, and four species were listed as national Class I key-protected plants. In the tropical low-land rainforest, indices of Simpson (D), Shannon-Wiener (H＇) and Evenness (E) were 0.9446, 5.696 and 0.7697, respectively, while for tropical montane rainforest, D, H＇and E were 0.9885, 6.9619 and 0.8807, respectively, and those of tropical montane dwarf forest were 0.9405, 4.7110 and 0.8737, respectively. The results showed that the tropical low-land and montane rainforest in the enlarged area had been restored well after many years of protection.