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Still a long way.....

Pakistan is the member of the following international organizations,

1. African Union/ United Nation Hybrid Operation in Darfur (UNAMID)
2. Asian Development Bank (ADB) in 1966 and since then has become ADB’s largest recipient in both number of loans and volume of assistance received—over 19.8 billion USD in loan to fund development from hydrostatic projects to banking for the poor, with about 14 million $ disbursed as the end of 2008.
3. Association of Southeast Asian Nations Regional Forum (ARF) on July, 2nd 2004.
4. Colombo Plan in 1950. (Colombo Plan is a regional organization that embodies the concept of collective inter-governmental efforts to strengthen the economy & social development of member countries in the Asia-Pacific Region. The primary focus f all Colombo Plan activities is on human resource development )
5. Commonwealth of Nations. Joined in 1947 (left in 1972 & rejoined in 1986)
6. Central Treat Organization (CENTO), original name was Middle East Organization or METO also known as the Baghdad Pact, was adopted in 1955 by Iran, Iraq, Pakistan, Turkey and the United Kingdom. It was dissolved in 1979. US pressure & promises of military and economic aid were in the negotiations leading to the agreement although UN could not initially participate “for purely technical reasons of budgeting procedures” In 1958, the United States joined the military committee of the alliance. It is generally viewed as one of the least successful of the Cold War Alliances.
7. Economic Cooperation Organization (ECO) is an inter-governmental regional organization established in 1985 by Iran, Pakistan & Turkey for the purpose of sustainable Socio Economic development of the member states. ECO is the successor organization of Regional Corporation for Development (RCD). In 1964 Pakistan signed the RCD Pact with Turkey & Iran, when all three countries were closely allied with USA—and as neighbors of the Soviet Union, wary of Soviet expansionism. To this day, Pakistan has a close relationship with Turkey. RCD became defunct after the Iranian revolution. In 1985, Pakistan-Turkish initiative led to the founding of the ECO, an organization that also includes Afghanistan, Azerbaijan, Iran, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan.
8. Food & Agriculture Organization (FAO) on September 7, 1947.
9. Group of 24 in 1971
10. Group of 77 (1976-1977, 1992-2009)
11. International Atomic Energy Agency (IAEA) on May 2nd 1957.
12. International Bank for Reconstruction and Development (IBRD) in 1952
13. International Chamber of Commerce (ICC) in 1955.
14. International Civil Aviation Organization (ICAO) on November 25, 1947.
15. International Criminal Court (ICCt)
16. International Criminal Police Organization (Interpol) in May, 1952.
17. International Development Association (IDA) in 1962.
18.International Federation of Red Cross and Red Crescent Societies (IFRCS)
19. International Finance Corporation (IFA) in 1955.
20. International Fund for Agricultural Development (IFAD) in 1978.
21. International Hydrographic Organization (IHO)
22. International Labour Organization (ILO) in 1947.
23. International Maritime Organization (IMO) in 1958.
24. International Mobile Satellite Organization (IMSO) on February 6,1985.
25. International Monetary Fund (IMF) in July 1950.
26. International Olympic Committee (IOC) in 1948.
27. International Organization for Migration (IOM) in November 1992.
28. International Organization of Standardization (ISO)
29. International Telecom Union (ITU) on 26th August 1947.
30. International Telecommunication Satellite Organization (ITSO)
31. International Trade Union Confederation (ITUC)
32. Inter Parliamentary Union (IPU) in 1948.
33. Islamic Development Bank (IDB) is a multilateral development financing institution located in Jeddah, Saudi Arabia. It was founded by the first conference of Finance Ministers of Organization of Islamic Conference (OIC) convened 18 December 1973. The bank officially began its activities on 15 Shawwal 1395 H (20 Oct. 1975). There are 56 shareholding member states. Pakistan joined IDB in
34. Multilateral Investment Guarantee Agency (MIGA) in 1991
35. Non aligned Movement (NAM) in 1977.
36. Organization of Prohibition of Chemical Weapons (OPCW) in 1993.
37. Organization of American States (OAS) Pakistan is an observer. In January 6, 1988.
38. Organization of Islamic Conference (OIC) is an international organization with permanent delegation to UN. It groups 57 member states from the Middle East, Africa, Central Asia, Caucasus, Balkans, Southeast Asia. Pakistan joined in 1969.
39. Partnership for Peace (PFP)
40. Shanghai Cooperation Organization (SCO) is an intergovernmental mutual security organization which was founded in 2001 in Shanghai by the leaders of China, Kazakhstan, Kyrgyzstan, Russia, Tajikistan and Uzbekistan. Except for Uzbekistan, the other countries had been the member of Shanghai Five, founded in 1996; after the inclusion of Uzbekistan, the members renamed the organization. Pakistan joined SCO in 2006 as an observer.
41. South Asia Co-operative Environment Program (SACEP) in 1982.
42. Southeast Asia Treaty Organization (SEATO) was an international organization for collective defense which was signed on September 8, 1954. The former institution was established at a meeting of treaty partners in Bangkok in February 1955. It was primarily created to block further communist gains in Southeast Asia. The organization’s headquarter was located in Bangkok, Thailand. SEATO was dissolved on June 30, 1977
43. South Asian Association for Regional Cooperation (SAARC) is an economic and political organization of eight countries Southern Asia. In terms of population, its sphere of influence is the largest of any regional organization; almost 1.5 billion people, the combined population of its member states. It was established, on December 8, 1985 by Bangladesh, Bhutan, Maldives, Pakistan, India, and Nepal & Sri Lanka. In April 2007, at the association’s 14th summit, Afghanistan became its eighth member. Pakistan joined SAARC in 1985. The Objectives of this organization are following,
a. To promote the welfare of the people of South Asia and to improve their quality of life.
b. To accelerate the economic growth, social progress and the cultural development in region and to provide all the individuals the opportunity to live in dignity and to realize their full potential.
c. To promote and strengthen the collective self reliance among the countries of South Asia.
d. To contribute the mutual trust, understanding and appreciation of one another problems.
e. To promote active collaboration and mutual assistance in the economic, social, cultural, technical and scientific fields.
f. To strengthen cooperation with other developing countries.
g. To strengthen cooperation among themselves in international forums on matters of common interests, and
h. To cooperate with international and regional organization with similar aims and purposes.
44. United Nations in 1947.
45. United Nation Conference on Trade and Development (UNCTAD)
46.United Nations Education, Scientific and Cultural Organization (UNESCO) on 14th September 1949.
47. United Nations High Commissioner for Refugees (UNHCR) in 1976.
48. United Nations Industrial Development Organization (UNIDO) in 1968.
49. United Nations Integrated Mission in the Sudan (UNIMS)
50. United Nations Observer Mission in Georgia (UNOMIG) on 23rd July 1995
51. United Nations Operation in Cote d’vloire (UNOCI)
52. United Nations Organization Mission in Democratic Republic of the Congo (MONUC)
53. Universal Postal Union (UPU) on 10-11-1947.
54. World Confederation of Labour (WCL)
55. World Customs Organization (WCO)
56. World Federation of Trade Unions (WFTU)
57. World Health Organization (WHO)
58. World Intellectual Property Organization (WIPO) in 1977.
59. World Metrological Organization (WMO)
60. World Tourism Organization (UNWTO)
61. World Trade Organization (WTO) in 1995

I have tried my best to compile above list but if you find any mistake then please point out and if i have missed any international organization in which Pakistan is participating as a member then please mention that ones as well.