The trial was the first in the world to centre on the agency's controversial programme, in which "terror" suspects are thought to have been transferred to countries known to practise torture.
The case concerned the seizure of Osama Moustafa Hassan Nasr, also known as Abu Omar, and his transfer to Egypt, where he claims he was tortured.
All of the Americans were tried in absentia, with 22 sentenced to five years in jail and Robert Seldon Lady, the Milan CIA station chief, handed eight years in prison.
Two Italians were given three-year prison terms.
Citing diplomatic immunity, Judge Oscar Magi told the Milan courtroom on Wednesday that he was acquitting three other Americans.
Five Italians, including Nicolo Pollari, the former head of Italy's Sismi military intelligence service, and Marco Mancini, his ex-deputy, were acquitted, with Magi saying that the men were protected by state secrecy rules.
Lawyers for the 23 Americans said they would appeal against their convictions.
Ian Kelly, a spokesman for the US state department, said of the judge's decision: "We are disappointed by the verdicts against the Americans and Italians charged in Milan for their alleged involvement in the case involving Egyptian cleric Abu Omar.
George Little, a CIA spokesman, told Al Jazeera that "the CIA has not commented on any of the allegations surrounding Abu Omar".
Al Jazeera's Claudio Lavanga, reporting from Milan, described the verdict as "quite shocking and unexpected".