The chemical compositions and functional properties of Zanthoxylum chalybeum (Knob wood) leave essential oils varied as growing locations. In this study, the variation in chemical composition and antimicrobial activities of the hydro distilled essential oils of the plant fresh leaves collected from three different growing places in Eastern Ethiopia (Awale, Dire Dawa Administration; Awaday, Haramaya subdistrict, and Lange, Kersa Subdistrict, East Hararghe Zone of Oromia Region), were investigated. The chemical composition of the respected essential oils, as determined by the GC-MS analysis, 13, 12 and 17 compounds representing 99.98%, 100.00% and 100.00% of the total leaves essential oil from the plant growing in Awale, Awaday, and Lange, respectively, were identified. The essential oils of Awale, Awaday and Lange were mostly β-phellanderene (23.96%, 45.31%, 23.45% respectively), whereas highest amount of other components in the essential oils of Lange: terpine-4-ol (25.02%) and sabinene (11.73%); Awaday: α-phellanderene (12.85%) and Awale: the sole β-myrcene (29.33%) was identified. In vitro antimicrobial activity in 20 μL dose of each essential oil evaluated by the disc diffusion method indicated strong antibacterial activities against the test bacteria (S.thyphi, Str. agalactia, S.aureus and E.coli ) and slight antifungal activities against the test fungi (A.niger, F.oxysporium). The essential oils' major constituents, the monoterpenoids, such as phellandrenes (α and β), terpinen-4-ol and sabinene could be responsible for the significant antimicrobial activities in this study. The plant essential oils' chemical composition and the antimicrobial activities significantly differ with growing locations. The findings confirm the plant's medicinal properties in traditional uses. The results open the many possibilities for further research on biocidal and antimicrobial activities of the essential oil and its individual components of the species growing in different regions of Ethiopia.
