An ethnobotanical study of medicinal plants was conducted to document the indigenous plant-based medical knowledge of the people of Goma Wereda in southwestern Ethiopia from September, 2009 to May, 2010. A total of 100 informants (73 males and 27 females) between the ages of 20 and 80 were selected to collect information on medicinal plant use from ten sampled kebeles. Out of these, 24 key informants (22 males and 2 females) were purposively selected based on recommendation from elders and local authorities. Other informants were selected randomly. Data were collected using semistructured interviews, field observations and group discussions. Informant consensus, preference ranking, paired comparison, direct matrix ranking, informant consensus factor (ICF) and Jaccard’s coefficient of similarity were calculated. A total of 160 plant species: 101 species from wild vegetation and 59 species from home gardens distributed in 124 genera and 58 families were collected and identified. Of these, 121 medicinal plant species were used as cure for 102 ailments. From these, 92 species were recorded for the treatment of human health problems, 12 species for livestock and 17 species for the treatment of both human and livestock. From the total medicinal plants species 54 species of the medicinal plants were herbs, followed by 30 species of shrubs, 26 species of trees and 11 species of climbers. The most frequently used plant parts were leaves (61.66%) followed by roots (13.33%). The most widely used method of preparation was crushing (26.80%) of the different plant parts followed by squeezing (22.68 %) and burning (7.21%). The common route of administration recorded was oral (52.01%) followed by dermal (28.52%) and nasal (8.3 %). The most commonly used application of medicinal plant was drinking (43.37%) followed by painting (10.84%) and put on and washing accounted for 10.84% each. The medicinal plants that are presumed to be effective in treating certain diseases such as Ocimum lamiifolium and Croton macrostachyus have high informant consensus. The disease categories such as rheumatism and stabbing pain as well as the categories of evil eye and evil spirit have higher ICF value of 0.907. Preference ranking showed that people of the area have preference for Acmella caulirhiza for the treatment of tonsillitis. Paired comparison of five species of plants that are used for the same disease showed that Indigofera spicata is the most preferred species by traditional healers for the treatment of insect allergy (‘Hadha’). Direct matrix ranking showed Cordia africana as the most utilized species by the community. Agricultural expansion, firewood collection, timber production and construction are major threats to plants in general and medicinal plants in particular in the study area. The participation of the local people, awareness raising through training or education on sustainable utilization and management of plant resources, establishment of forest protected areas should be encouraged. Key words: Ethiopia, Ethnobotany, Goma. homegardens, informant consensus factor