The proposal offers Iran economic and trade incentives but also calls on Tehran to suspend uranium enrichment activities, which world powers fear could be used to make a nuclear weapon.
Solana arrived at Tehran's city airport at 11:00 pm (1830 GMT) without speaking to reporters, an AFP correspondent reported.
"I am travelling to Tehran to present a generous and comprehensive offer," he said before leaving Brussels.
"With this offer, the EU and the six countries I represent show their desire to develop a constructive and cooperative relationship with Iran in the nuclear field and in many other areas," he added.
It already appears unlikely Iran's leaders will accept a suspension of uranium enrichment activities, especially after repeated vows from President Mahmoud Ahmadinejad that Tehran will never back down in the standoff.
"They think they can trample on the Iranian nation's dignity with such things," Ahmadinejad said on Wednesday. "If they want to give us something, then they should sell it and we will buy it," he added.
Solana, who has warned not to expect "miracles", is due to present the offer on Saturday in talks with Iran's Foreign Minister Manouchehr Mottaki and the chief nuclear negotiator Saeed Jalili.
Conspicuously, it appears that no meeting with the hardline Ahmadinejad has been scheduled.
Solana is presenting the offer on behalf of the five permanent UN Security Council members plus Germany, on behalf of whom he has led a hitherto fruitless set of discussions with Tehran for the past two years.
Representatives of five of the six main powers involved in the drawn-out negotiations — Britain, China, France, Germany and Russia — will also take part in the talks.
The sixth power, the United States, has had no diplomatic relations with Iran since 1980.
In their offer, the six major powers "recognise Iran's right to develop research, production and use of nuclear energy for peaceful purposes, purposes in conformity with non-proliferation treaty (NPT) obligations."
But it also calls on Iran to comply with four UN Security Council resolutions — including three linked to existing sanctions — which call for the suspension of its nuclear enrichment activities
The proposal is a "refreshed" version of an offer initially presented by Solana in June 2006 which Tehran rejected.
The new offer "has been structured a bit differently, but the substance could not be changed because it is already very strong," a European diplomat said. "We can't go too far."
The powers offered in 2006 to help Iran develop "more modern" technologies and to supply Tehran with enriched uranium for civil purposes.
In 2006 the offer was also on the table to allow Iran to improve its ageing fleet of Boeing airlines for civil aviation. Spare parts are currently under embargo.
For the first time, Solana will be handing offer a "policy" letter signed by the foreign ministers of all six powers.
In it the ministers declare themselves "convinced that it is possible to change the present state of affairs," and "hope that Iran's leaders share the same ambition," according to a section of the letter seen by AFP.
Iran, OPEC's number two producer, vehemently rejects Western allegations that it is seeking nuclear weapons, saying it wants only electricity for a growing population whose fossil fuels will eventually run out.
But the United States and Iran's arch regional foe Israel have never ruled out military action against Tehran to end its defiance in the nuclear standoff.
US President George W. Bush, on his trip to Europe this week, warned of further sanctions against Tehran and also said "all options" were still open over how to end the crisis.
