The study examines the historical development of Nigerian peacekeeping mission under the auspices of the United Nations Security Council from 1960 to 2009 using Sierra Leone as a case study. Furthermore, it discusses the concept, nature and general principles of peacekeeping; examined the foreign policy objectives of Nigeria in relation to her peacekeeping mission; examine the contributions of Nigerian peacekeeping mission to the installment of peace and stability in Sierra Leone between 1991 and 2000; and review the major challenges facing Nigeria peacekeeping mission. Historical research method was employed in this study. Both primary and secondary source materials were used by the researcher. The study established that Nigeria’s peacekeeping mission has been beneficial to the country especially in the projection of her public diplomacy and foreign power abroad.