The UN officially came into existence on 24 October 1945 , after ratification of the United Nations Charter by the five permanent members of the United Nations Security Council ( the Republic of China , France , the Soviet Union , the United Kingdom , and the United States ) and a majority of the other signatories . A total of 51 original members ( or founding members ) joined that year ; 50 of them signed the Charter at the United Nations Conference on International Organization in San Francisco on 26 June 1945 , while Poland , which was not represented at the conference , signed it on 15 October 1945
United Nations Conference on International Organization
United Nations Conference on International Organization
Member states of the United Nations