The decision was made by existing members, including China, Britain, France, India and Italy
Iran has been accepted as a founding member of the China-led Asian Infrastructure Investment Bank (AIIB), Chinese state news agency Xinhua reported late on Tuesday.
The decision was made by existing members, including China, Britain, France, India and Italy, it added.
The United Arab Emirates has also been accepted, Xinhua said.
The AIIB is seen as a potential rival to established lenders the World Bank and Asian Investment Bank, which are dominated by the United States and Japan.
China and Iran have close diplomatic, economic, trade and energy ties.
AIIB will prioritise funding for infrastructure projects in Asia, while creating a new platform for regional and international cooperation to support developing Asian countries.
The bank will focus energy and power, transportation, telecommunications, rural infrastructure, agriculture development, water supply and sanitation, environmental protection, urban development, and logistics.