What is the capitol city of Iran?

The capital of Eye-Ran is Tehran.

Capital Is Tehran 

Capital city, not capitol city. And you can easily look this up instead of wasting our time here. Sod off.

Salt Lake Citey

Tehran is the capital of Iran and Tehran Province.

The United States Capitol, often called the Capitol Building, is the meeting place of the United States Congress and the seat of the legislative branch of the U.S. federal government. It is located on Capitol Hill at the eastern end of the National Mall in Washington, D.C. Though no longer at the geographic center of the federal district, the Capitol forms the origin point for the district's street-numbering system and the district's four quadrants.

Tehran.  As others have pointed out below, "capital" is for the capital city; "capitol" actually is the building.  So the US Congress meets in the capitol, which is inside the capital.

Please, first, note the correct spelling is 'capital'. The capital, and largest city, of [the Islamic Republic of] Iran is Tehran.

Tehran is the capitol.

Tehran is the capitol city of Iran (according to google).

The capital of Iran is "Tehran."