Ambassador (retired) Oluyemi Adeniji (born July 22, 1934 in Ijebu Ode, Ogun State) is a Nigerian career diplomat and politician who was the Special Representative of the General Secretary with the United Nations Mission in Sierra Leone (UNAMSIL) from November 19, 1999 to July 16, 2003. Later he was Foreign Minister of Nigeria from July 2003 to June 2006, then Internal Affairs Minister from 21 June 2006 to May 2007.

Adeniji has a degree in History. He joined the Nigerian Foreign Service in July 1960. He served in the Ministry of Foreign Affairs and Nigerian embassies in Washington, D.C., Freetown, Sierra Leone, and Accra, Ghana. He retired from service in 1991 after serving as the Director-General of the ministry of foreign affairs. For five years he was the Nigerian Ambassador to France.

He was the United Nations Secretary-General's Special Representative for the United Nations Mission in the Central African Republic (MINURCA). The mission was responsible for providing security in Bangui and for coordinating the legislative and presidential elections held in 1998 and 1999. He was then appointed the United Nations Secretary General's Special Representative for Sierra Leone and Head of the United Nations Mission in Sierra Leone (UNAMSIL).