The daughter of influential former Iranian president Akbar Hashemi Rafsanjani was taken to prison late on Saturday to serve a six-month sentence for "spreading anti-state propaganda," Iranian media reported.
Faezeh Rafsanjani, a former member of parliament, was convicted in January and sentenced to jail.
The conviction is believed to be over an interview she gave to an opposition news site in which she criticised human rights violations and economic policy in Iran.
Gholamhossein Esmaili, Iran's prisons chief, was quoted by the Mehr news agency as saying she was taken to Tehran's Evin Prison.
She was detained briefly in 2009 after street protests against the election that returned President Mahmoud Ahmadinejad to power. Protesters said it was rigged in favour of the incumbent. Faezeh had addressed supporters of defeated candidate Mirhossein Mousavi, who had gathered in defiance of a ban on opposition protests.
Her latest detention comes as her brother Mehdi Rafsanjani is expected to return to Iran after living and studying in the United Kingdom. Officials have said Mehdi should be arrested upon arrival in Iran, accusing him of fomenting unrest after the 2009 vote.
An independent source told Reuters Mehdi was in Dubai and expected to return to Iran on Sunday.
The wealthy Rafsanjani family has faced heightened pressure from hardliners since the 2009 vote, which set off the deepest political crisis and worst unrest in Iran since the 1979 Islamic Revolution.
The centrist Akbar Hashemi Rafsanjani, one of the founding figures of the Islamic Republic and a close aide to the revolutionary leader Ayatollah Ruhollah Khomeini, expressed sympathy for opposition demonstrators and saw his own power and influence wane as a result.
In March 2011, he lost his post as head of the state clerical body, the Assembly of Experts, consolidating the ascendancy of the hardline Ahmadinejad.