請問在1945年全世界共有多少個國家? 謝謝!

您好
比較接近的數字是1945年底簽署憲章、參與聯合國的國家有51個. 
若有新的資料， 再行奉告.

In 1945， the UN had 51 members.
The UN officially came into existence on 24 October 1945 upon ratification of the Charter by the five permanent members of the Security Council—France， the Republic of China， the Soviet Union， the United Kingdom and the United States—and by a majority of the other 46 signatories. The first meetings of the General Assembly， with 51 nations represented， and the Security Council， took place in Westminster Central Hall in London in January 1946]

Wikipedia_United Nations
Wikipedia_United Nations  General Assembly