Dissertation (MSc. Biodiversity Conservation)A study was conducted at Marumbi and Uroa villages of Central District of Unguja Zanzibar to assess diversity of medicinal trees species based on specific objectives: (1) to determine diversity of medicinal tree species in the two study village forests; and (2) to determine extent of extraction of medicinal trees: A total of 99 circular plots (radius, r= 11.28 m) were laid down systematically. Medicinal trees were identified and recorded against tree tally, and computed for indices of diversity. Extent of extraction of medicinal trees was assessed using a socio-economic survey. Semi-structured questionnaires, matrix ranking and interviews were administered among 48 local community including traditional healers and herbal medicine dealers. A total of 55 medicinal trees species which belong to 28 families were identified. Shannon-wiener index (H’) ranged from 1.44 to 2.899 for Marumbi forest, and from 1.519 to 3.106 for Uroa forest. Simpson index of diversity (D) ranged from 0.108 to 2.287 and from 0.137 to 0.327 for Marumbi and Uroa forests, respectively. The Simpson index of dominance (C) value ranged from 0.14 to 0.13 at Uroa, and from 0.18 to 0.14 for Marumbi forest. The most dominant species were Polysphaeria porvofolia, Macphersonia gracilis, Euclea natalensis and Suregada zanzibarensis. Rare species were Drypetes natalensis, Croton sylvaticus and Vernonia zanzibarensis. Results revealed over exploitation of medicinal trees in the two forests. Based on the inherent knowledge of local communities, Croton sylvaticus, Drypetes natalensis, Pittosporum viridiflorum, Vernonia zanzibarensis and Teclea simplicifolia were ranked as priority medicinal tree species. It can be concluded that, the ongoing overexploitation of the medicinal trees could threat sustainability of medicinal tree species.