APTA: History

1975 Bangkok agreement is signed as an initiative of the United Nations Economic and Social Commission for Asia and the pacific (UNESCAP). The six founding nations are Bangladesh, India, the Republic of Korea, Laos, and Sri Lanka.
China becomes a member to the Bangkok Agreement. 2001
2005 Bangkok agreement formally renamed the Asia-Pacific Trade Agreement (APTA).
Mongolia becomes a member of APTA. 2013

Sources

United Nations ESCAP Trade and Investment

Glossary