Iranian dissident Hashem Aghajari has had his jail term reduced to three years from eight years, but the courts have yet to decide if he will still hang on blasphemy charges.
An additional punishment of 74 lashes was also commuted to an unspecified fine, they said.
Aghajari, condemned on November 6, 2002 behind closed doors by a court in the western city of Hamedan for blasphemy, was transferred to Tehran to begin his three-year prison term, while waiting for the Hamedan court to decide whether to commute the death sentence.
He was also given a week of leave before starting his time in prison to visit his family.
Aghajari, a disabled veteran of the Iran-Iraq war and supporter of reformist President Mohammad Khatami, sparked the anger of Iran's religious establishment in a speech on June 19, 2002.
He questioned clerics' right to rule in Iran, calling for an "Islamic Reformation" and saying that Muslims "should not blindly ... follow their religious leaders".
But even some conservatives criticised the heavy sentences handed down, whole reformists and students held a series of protests, until Iran's supreme leader Ali Khamenei on November 17 ordered the sentence to be revised.
Iran's supreme court overturned the verdict in February, due to flaws in the judicial investigation. If the original death sentence is confirmed, the case will be sent back to the supreme court.