在冷戰期間，國際政治深受美、蘇對峙所影響，其中聯合國是雙方交鋒的重要戰場，這嚴重影響了聯合國的正常會務發展。聯合國在1945年建立時共有51國名列創始會員，但在此後的10年間，先後有20餘國的入會申請案由於冷戰等政治因素影響而擱置。直到1953年史達林過世以後，入會問題才透露出解決的曙光。1955第十屆大會期間，加拿大主導推動了一項包括18國的整批入會方案，讓大部分提出過申請的國家，不論其政治屬性皆能同時入會。這項計畫因爲有助於打破會籍問題僵局而獲得會員國的壓倒性支持，但整批國家名單中的外蒙古引發了複雜的政治效應。在掌握入會問題關鍵的常任理事國中，中華民國堅決反對外蒙入會，蘇聯則強調除非全部否則就一個都不能入會的立場。美國做爲臺灣的主要政治盟友，其立場極爲困難。雖然各方爲突破僵局進行過許多的討論，案件仍在安理會的投票中遭到蘇聯與中華民國的否決。但就在入會案破局的隔日，蘇聯突然另提一個精簡掉外蒙與日本的整批入會案，並迅速得到安理會與大會的通過，使入會僵局在1955年有所突破，是聯合國邁向會員普及化的重要關鍵。
本案既是觀察冷戰期間國際政治發展的重要窗口，同時也是中華民國外交史的重要一頁，對臺美外交關係、臺灣在聯合國的地位等皆多有牽動。本文主要以外交檔案與聯合國文件爲材料，經由比對各方立場與言論，重建事件的經過。在美、蘇爭霸的框架下探討各國間複雜的互動關係，希望藉此拓展對冷戰時期國際政治與中華民國外交的認識。

During the Tenth General Assembly of the United Nations in 1955, the general debate on the admission of new membership had become the focus of international politics. Since the United Nations was founded in 1946, more than 20 countries' membership applications were laid on the table due to the perplexing political situation during the Cold War. Nevertheless, the death of Stalin in 1953 to some extent mitigated the tensive relationship between the United State and the Soviet Union, and brought an opportunity to solve the affiliation problem. Under this background, Canada proposed a resolution of admitting all 18 countries that had been applying for membership but failed. This proposal was supported by majority of members in the General Assembly. However, it also confronted two crucial issues in the Security Council. On the one hand, the government of Republic of China tended not to recognize the independent status of People's Republic of Mongolia, and therefore against Mongolia's affiliation. On the other hand, the Soviet Union strongly insisted a package deal including Mongolia, that is, all 18 or none. As a result, the affiliation cases were voted by both Soviet and republican China in the Security Council. While this dilemma seemed to be irresolvable, the Soviet Union suddenly proposed a new draft resolution admitting 16 nations' memberships except Japan and Mongolia. This new proposal was adopted by the Security Council and the General Assembly promptly on the very same day. All in all, this case offers us a window to look into the historical development of the United Nations and the diplomatic history of Republic of China as well as to observe the complicity of the Cold War polities.