On 25 April 1945 , the United Nations Conference on International Organization began in San Francisco . In addition to Governments , a number of non-government organizations , including Rotary International and Lions Clubs International received invitations to assist in the drafting of a charter . After working for two months , the fifty nations represented at the conference signed the Charter of the United Nations on 26 June . Poland , which was unable to send a representative to the conference due to political instability , signed the charter on 15 October 1945 . The charter stated that before it would come into effect , it must be ratified by the Governments of the Republic of China , France , the USSR , the United Kingdom , and the United States , and by a majority of the other 46 signatories . This occurred on 24 October 1945 , and the United Nations was officially formed
United Nations Conference on International Organization
United Nations Conference on International Organization
History of the United Nations