Palestinian attackers kidnapped the Italian - identified as Alcandro Pero, a peace activist - on Sunday afternoon in the town of Khan Yunus, witnesses said.
"He has been freed," an Italian member of the European parliament, Luisa Morgantini, said by telephone from the Gaza Strip.
Morgantini said she learned of his release through indirect contacts with the kidnappers.
Pero was being driven back to Gaza City after his ordeal, Palestinian security sources confirmed.
He was kidnapped earlier on Sunday, when armed men in two cars stopped a minibus carrying 10 foreigners as it was driving through the town, forced him out and into one of their vehicles before speeding away to an unknown destination, other passengers said.
Pero was part of a delegation of 19, which included European parliament members and teachers who were visiting Gaza.
The group was to visit the election campaign office of Salam Fayad, Palestinian Legislative Council candidate, former finance minister and head of the Third Way list.
There was no immediate claim of responsibility, and Palestinian officials were not immediately available for comment.
Residents of the Khan Yunus neighbourhood where the kidnapping happened took to the streets to protect the rest of the delegation.
"This is simply unacceptable. Not enough is being done to prevent these atrocities from taking place," Abo Mohammad of Khan Yunus told Aljazeera.net.
The abduction is the latest in a rash of kidnappings in Gaza since Israel's withdrawal from the coastal strip in September.
British aid worker Kate Burton was
captured along with her parents
On Friday, three Britons were released after being held by gunmen for two days.
Palestinian security officials said the Britons were abducted by gunmen with ties to Palestinian leader Mahmoud Abbas' ruling Fatah party.
The kidnappers said they were members of a previously unknown group, the Mujahidin Brigades' Jerusalem Branch.
Foreigners have been kidnapped as bargaining chips to get relatives released from Palestinian prisons, secure jobs from the Palestinian Authority, or settle personal scores.
The kidnappings have all been relatively brief and all the hostages have been released unharmed.
Laila el-Haddad, Aljazeera.net's correspondent in the Gaza Strip, contributed to this report.