Tanzania is endowed with more than 10,000 plant species, of which 1,100 are endemic. The coastal regions host most endemic species, due to its wide range of productive ecological conditions. Over 25 % of all species are used as wild-harvested medicinal plants. About 60% of the Tanzanian population in both rural and urban areas depends on traditional medicine and herbs as their primary health care, and as a means of generating income. This is due to high costs and unavailability of the universal healthcare, which was abolished in 1993. The aim of the thesis is to make a structured and a quantitative investigation to identify traded medicinal plants traded in markets of Dar es Salaam in Tanzania with a purpose to understand the chain and consequences of commercial trade on wild-harvested medicinal plants. A quantitative market research using free list surveys was used in combination with individually repeated in-depth structured and semi-structured interviews. Furthermore, Conservation Assessment and Planning Management method was used to prioritise species that are in need of conservation due to commercial trade. The results show that the chain of commercial trade of medicinal plant species begins in the forest and is then distributed to different stakeholders, such as harvesters, vendors, Traditional Healing Practitioners, consumers and exporters. The research also shows that the large urban and international demand of medicinal plant species supplied by the vendors and exporters is the major threat, specifically to destructively harvested species such as Cassia abbreviata, Zanthoxylum usambarense, Zanthoxylum chalybeum, Myrsine africana, Milicia excelsa and Prunus Africana. These medicinal plants species are up-rooted and/or ring-barked and are therefore in need of conservation. This calls for several conservation guidelines such as policy and regulations, Traditional Ecological Knowledge, education and planting of the medicinal plant species in their natural forests as well as collecting samples of medicinal plant species in a herbarium. Policies can be implemented to conserve these species, for instance only allowing registered practitioners to harvest the medicinal plant species to a level that will sustainably balance the quantity of medicinal plant species in the forest and its supply. In conclusion, an important policy regulation could be an export tax on internationally-traded wild-harvested medicinal that is levied on the purchasing international pharmaceutical companies, which would then be used to fund the conservation of the medicinal plant species to retain a sustainable wild stock. More investigation on the actual population sizes of these plant species is needed in order to secure their existence and contribute to sustainable development both socially and environmentally