"We must guarantee that the People of Freedom is not the party of one person, but of one country."
AN has been allied with Forza Italia since the mid-1990s and ran under a single banner in last year's election, helping the media tycoon win a landslide victory and a third term in office.
The alliance gave AN four ministers in the coalition government.
"Today a long chapter in the life of Italy's post-war right comes to an end"
National Alliance leader
But despite the close ties between the two parties there have been lingering rivalries between the leaders.
Fini has spoken out against the government's crackdown on illegal immigration and of Berlusconi's growing use of emergency decrees to rush legislation through parliament.
The National Alliance was the successor to the Italian Social Movement formed by supporters of Benito Mussolini, Italy's second world war fascist leader, after he was killed in 1945.
Fini once described Mussolini as the greatest statesman of the 20th century, but he has since distanced himself from AN's more hardline supporters.
He has also branded laws which discriminated against Jews, brought in under Mussolini's rule, as "a shameful page in our history".
"We have come to terms with our past, we have said clear words of condemnation over Italian history between the two wars. Today a long chapter in the life of Italy's post-war right comes to an end," Fini said on Sunday.
Some commentators have suggested that Fini wants to take over from Berlusconi if the 72-year-old should decide to retire from politics.