Abstract: In the report， in order to further definite the characteristic differences between the natural mangrove forests in northeastern and that in the northwestern of Hainan， the field survey on the mangrove forests in the two areas were performed. The results indicated that the species composition of mangrove forests in the northeast is richer than that in the northwestern. 15 families and 24 species of natural mangrove plants are recorded in the northeast， including 10 families and 18 species of true mangroves and 5 families and 6 species of semi-mangroves， 12 families and 16 species are recorded in the northwest， including 7 families and 11 species of true mangroves and 5 families and 5 species of semi-mangroves. The community types of the northeastern is more abundant than that of the northwestern. 16 natural mangrove community types are obtained in the northeast and only 8 in the northwest. Bruguiera gymnoihiza， Bruguiera sexangula and Rhizophora stylosa are dominant in the northeast， Rhizophora stylosa， Avicennia marina and Aegiceras corniculatum are dominant in the northwest， mostly as shrubs. The species diversity in the northeast is higher than that in the northwest. In the northeastern， the range of diversity indices for each species mangroves are species richness index R （17 ~ 24）， Shannon-Weiner index H （1.33 ~ 1.42）， Simpson index D （0.66 ~ 0.71）， and Pielou evenness index E （0.79 ~ 0.87）， and in the northwestern， the index is R （8 ~ 16）， H （0.31 ~ 1.07）， D （0.19 ~ 0.57）， and E （0.34 ~ 0.80）， respectively. In short， the dominant species of natural mangroves in the northeast of Hainan are mainly arbors， but shrubs in the northwest. The plant composition， community types and species diversity of mangroves in the northeast are richer than that in the northwest. Our study provides the reference for the protection and development of mangrove resources in Hainan.