An ethnobotaniacal study of medicinal plants was carried out from October 20/2009 to Aprilrn15/2010 in Seru Wereda, Arsi Zone of Oromia Regional State, Ethiopia. The purpose of thernstudy was to identify and document medicinal plant taxa. Ethnobotanical information of thesernplant taxa was gathered through a semi-structured interview, field observation, group discussionrnand market survey. Eighty informants from twelve Kebeles were subjected to this study. Onernhundred and twenty one medicinal plant taxa belonging to 109 genera and 58 families werernreported and for each taxon a local name (Afaan Oromo) was documented. Plants, parts usedrnand methods of preparation were also documented in the current study. Out of these medicinalrnplants collected, 62(51.24%) were reported to treat human aliments, 14 (11.57%) livestockrnailments and 45 (37.19%) both human and livestock ailments. Ninety nine (81.82 %) of the plantrntaxa were collected from the wild and, 22 (18.18%) from home gardens. Herbs were found to bernthe most widely used life forms and this accounts for 53 (43.79%). This is followed by shrubsrnwith 37.18% (45 taxa). The most frequently used plant parts were reported to be the leaves,rnwhich is 64 taxa (41.03 %) and then the roots 25.64% (40). The most widely used method ofrnpreparation was reported to be crushing and pounding a single plant part or a mixture of plantrnparts of different taxa. The different use categories of medicinal plant taxa in the area includedrnfood, firewood, charcoal, construction and forage. Major conservation threats includedrnagricultural expansion, overgrazing, fire wood collection, charcoal production, cutting downrntrees for construction and furniture .There was no record that indicated the severe conservationrnimpacts of overharvesting of medicinal plants and their parts in the current study area.rnNoteworthy is that both cultural and spiritual beliefs positively contributed to the managementrnand conservation of medicinal plants of the study area. In addition to the aforementionedrnpositive attitude of the local communities to the conservation of natural resources,rnsupplementary environmental education with regard to sustainable uses of medicinal plantsrncould be useful.rnKey Word: Arsi Zone, Conservation, Ethnobotany, Indigenous knowledge, Medicinal plants,rnSeru Wereda