Bush encroachment has been among the major threats to the livelihood of Boranarnpastoralists and their ecosystem. A study was conducted in Yabello district to map bushrnencroachment using supervised classification and SMA (spectral mixture analysis).rnLandsat Thematic Mapper and Enhanced Thematic Mapper Plus images that were taken inrnJanuary 1986 and 2003 respectively, 33333were used to assess the land-use/land-coverrndynamics, to determine rate of bush encroachment and to spatially locate bush encroachedrnareas. Six land-use/land-cover types were defined for supervised classification. They werernforest, woodland, bushland, grassland, crop/cultivated land and bareland. Unconstrainedrnlinear SMA was run on the original DN image using woodland, bushland, Savannahrngrassland, tilled soil and bare surface endmembers. Endmembers collected from the fieldrnwere tested for their purity by applying pixel purity index and minimum noise fractionrntransform. Classification result and unmixing were assessed for their accuracy usingrnrandom samples collected from the field. Overall accuracy and Kappa coefficient forrnsupervised classification of the 2003 image were 82.66% and 0.778, respectively. For thernbush fraction image of 2003, they were 72.28% and 0.640, respectively. The study showedrnthat bushland, woodland and crop/cultivated land were increased and forest, grasslandrnand bareland were decreased between the study period. The rate of bush encroachmentrnwas 2.54% per year. Bush fraction image showed that in 2003 about 20% of the land wasrncovered by bushy species that had > 40% canopy cover. In Borana rangelands, wherernheterogeneous vegetation exists, spectral mixture analysis using woodland, bushland,rnsavannah grassland, bare surface, tilled soil and shade endmembers based on Landsatrnimages was found less promising to unmix the land-covers. However, it gave betterrnmeasure on the status of bush encroachment during 2003 than supervised classificationrnmethod. Among others, multiple endmember spectral mixture analysis based on highrnspectral resolution images is recommended to better unmix the land-covers.rnKey Words: Bush encroachment, supervised classification, SMA, endmember & Landsat