Haleh Esfandiari was released on $333,000 bail and was resting at her mother's Tehran home, The Washington Post reported.
Esfandiari, a 67-year-old grandmother, is director of Middle East programs at the Smithsonian's Woodrow Wilson Center. She was visiting her ailing 93-year-old mother when she was put under house arrest, then taken to the notorious Evin Prison on May 8.
Her release followed a letter expressing concern for her health sent by former U.S. Rep. Lee Hamilton of Indiana, president of the Woodrow Wilson Center, to Iran's Supreme Leader, Ayatollah Ali Khamenei.
The Post said Esfandiari was one of at least four U.S. citizens being held in Iran on vague charges.