It is the first such visit since Iran blocked access to the plant outside the central town of Arak in April.
"A group of inspectors are arriving today to inspect Arak and this is within the framework of what we agreed with the International Atomic Energy Agency (IAEA)," foreign ministry spokesman Mohammad Ali Hosseini was quoted by AFP Monday.
Iran had said on July 13th that it would let IAEA inspectors visit the Arak heavy water reactor, which is currently under construction and should be completed in 2009.
Its decision was seen as a conciliatory move at a time of mounting tension over the Iranian nuclear programme, which has already seen Tehran slapped with two sets of UN sanctions.
The United States fears the Arak reactor could provide plutonium for weapons but Iran insists that it will provide key nuclear technology for peaceful purposes.