The United Nations Organisation (UN) is best endowed to conduct preventive diplomacy (PD) by preventing disputes and conflicts arising from interstate and intrastate relationships. The UN has the means to prevent such conflicts and disputes from emerging and escalating into armed confrontation. This article examines the challenges faced by the United Nations as it practises PD with specific reference to Africa. The Charter of the UN sets out the legal basis of PD for the UN, and for regional and sub-regional organisations. Contributions of four UN Secretary-Generals on matters of PD are examined, and special note is taken of the way in which the current Secretary-General, Mr. Ban Ki-moon, uses a four-pronged approach to matters of PD in Africa. The UN has performed well in PD in Africa, especially in collaboration with sub-regional organisations. While the UN derives its mandate to conduct PD from Articles in its Charter, its options are limited to peaceful settlement of disputes, and its action is restricted by rules of international law on intervention, especially with regard to the prohibition of the use of force. The UN is challenged by its inherent problems such as its structures, and its lack of early warning systems and finances. Challenges arising from the principle of state sovereignty also limit the UN in preventing internal problems, especially at the pre-conflict stages. This article concludes by proposing that strengthening the Secretary-General’s good offices, enhancing conflict early warning systems and encouraging the international community to work together could give legitimacy to UN preventive diplomacy endeavours. Fundamentally, the realisation that violent political problems require political solutions is instrumental in order for the UN to play its PD role.