Indigenous knowledge on the use and conservation of medicinal plants by the Hehe ethnic group in the Udzungwa Mountains, Tanzania was documented through literature review, ethnobotanical survey, open-ended interviews, semi-structured questionnaires, village meetings and field observations. Twelve villages and 42 traditional healers were involved. At each village eight field transects were established. Eighty three medicinal plant species in 50 families were recorded. Medicines were extracted from one species or a mixture of several. Bark, roots, leaves, flowers, fruits and whole plants were used to prepare medicines. Traditional methods of conserving medicinal plants include social control of access (sacred groves), domestication, sustainable collecting and storage. Eastern Arc Mountains endemics are rarely used. Compared to other studies in the Eastern Arc Mountains, the number of overlapping medicinal plant species in different mountain blocks is less than 25% and those that do overlap are used for different purposes by various ethnic groups.