The present study was carried out in the rift valley of southern Ethiopia, which isrngenerally characterized by arid and semi-arid climatic conditions. Studies in the naturalrnvegetation of the area were conducted between October 24, 2003 and June 28, 2004. Thernvegetation and environmental data were collected from 55 quadrats (400 m ) of eightrnselected sites. The purpose of this study was to investigate the floristic diversity of naturalrnvegetation of Abaya Hamassa in ( he rift valley of southern Ethiopia. In this paper, thernmajor issues addressed include floristic diversity, vegetation description, community typernidentification and study of communities - environment relationships. During the study,rnpercentage cover abundance of each species was estimated and taken in 55 quadrats.rnLater the percent cover values of all recorded plant species was converted into thernmodified Braun-Blanquet 1-9 scale. The environmental parameters altitude, slope,rnaspect, pH, electrical conductivity, total nitrogen and soil texture (% sand, % clay and %rnsilt) were measured for all quadrats. A total of 315 plant species representing 198 generarnand 59 families were identified. All the environmental and vegetation data were analizedrnwith TW1NSPAN computer program. Six plant community types were obtained andrndescribed. Community-environment relationship was assessed based on some soilrnphysical and chemical properties data collected from 55 quadrats. Among thernenvironment parameters altitude is negatively correlated with sand and clay. There wasrnsignificant correlations between total nitrogen with sand.