This thesis reports the ethnobotanical study conducted on the medicinal plants, between August 2010 and October 2012, in Erob and Gulomahda districts in Tigray Region of Ethiopia. Ethnobotanical information on plants of local medicinal was gathered through semi-structured interviews involving 382 informants representing different social groups, group discussion, field observation, guided field walk and market survey. A total of 121 medicinal plant species, belonging to 100 genera and 52 families, used to treat 75 human and 27 livestock ailments were documented from both districts. In Erob, 85 plant species in 72 genera and 42 families claimed for treating 58 human and 24 livestock ailments were recorded while 102 medicinal plants in 88 genera and 48 families were documented from Gulomahda, which were claimed to treat 67 human and 18 livestock ailments. The Asteraceae, Solanaceae and Lamiaceae had 11 species each. The herb category was the dominant growth form in the study area. Plant species collected from the wild were the highest in both districts. The most frequently used plant part for preparation of remedies in both districts was the leaf. The local people of the study districts frequently engage their eloquent proverbs to accentuate the importance of plant species for medicinal purposes including the saying “a drug can kill, and a drug can save”, which survived for generations. Jaccard’s Coefficient of Similarity of Erob and Gulomahda for the reported traditional medicinal plants was 0.55 indicating some trend of using common plants. The insignificant mean number of plant species used to treat human (p (0.17) > 0.05) and those for livestock ailments (p (0.26) > 0.05) between the two districts showing that the local people use similar plant species to cure ailments. The insignificant different of χ2 test for the relation of gender on conservation of traditional medicinal plants in Erob (p (0.27) > 0.05) and Gulomahda (p (0.23) > 0.05) showing that conservation of medicinal plants was not affected by gender differences. The computed Pearson’s Correlation Coefficient for the knowledge among different age levels was 0.84 for Erob and 0.77 for Gulomahda showing a stronger positive (direct) linear relationship between age and knowledge in both districts and this relation was significant in Erob (p (0.00) < 0.05) and Gulomahda (P (0.00) < 0.05). A negative linear relationship for the knowledge among different educational leveles was 0.44 for Erob and 0.47 for Gulomahda indicating modern education affects the knowledge on medicinal plants and the relation was significant in Erob (P (0.00) <0.05) and Gulomahda (P (0.00) < 0.05). The insignificant difference for mean knowledge of medicinal plant between male and female in Erob ( p (0.39) > 0.05) and Gulomahda (p (0.08) > 0.05) indicating that males and females were equally responsible for primary healthcare of the members of their families. The significant difference for mean knowledge between Saho and Tigrigna speakers in Erob (p (0.02) < 0.05) indicating that the mean knowledge of Saho speakers is significantly greater than the mean knowledge of Tigrigna speakers for the reported medicinal plants in this District. The significant difference for the mean knowledge between Catholic and Orthodox followers in Erob (p (0.02) < 0.05) indicating that the mean knowledge for the reported medicinal plants by the Catholic followers) was significantly greater than those of Orthodox followers in this District. There was no widely observed trade on medicinal plants in the markets studied. Threats on medicinal plant species included drought, fuel wood collection, construction material extraction and civil unrest while rehabilitation of degraded areas, replanting, homegardening and provision of alternative energy sources are suggested as plausible actions to protect the medicinal plant resources and the associated indigenous knowledge. Key words Ethnobotany, ethnomedicine, ethnovetrinary medicine, Erob, Gulomahda, Tigray, Ethiopia