Mesic said that antifascists and those who had fought in the National Liberation War had created the foundations of independent Croatia, making it one of the winners of World War Two.
"You were on the side on which every honest man at that time should have been and this won't be diminished by the attempt to rehabilitate the defeated by making them the winners," said Mesic.
He condemned attempts to revise history, saying that the claim that the 1941-5 Independent State of Croatia (NDH) had been the precursor of today's Croatia was an unfounded lie.
"The NDH wasn't independent. It was founded on crime, it was an unfortunate episode and a disgrace for the whole Croatian people," the president said to the applause of those in attendance.
"Croatia mustn't let anyone hold it hostage to the past," he said, adding that some prominent Croatian politicians, including some in the Parliament, should read history text books.
The president opposed attempts to proclaim the supreme commander of the National Liberation Army, Josip Broz Tito, a criminal, saying that Croatia must not allow this.
The president of the Alliance of Antifascist Fighters and Antifascists of Croatia, Kresimir Piskulic, said that given its size and 200,000 fighters, Croatia had built up the biggest resistance movement against fascism and Nazism in Europe.
He supported Mesic's and Prime Minister Ivo Sanader's antifascist positions and commended the adoption of a parliamentary declaration on antifascism. He said the decisions of ZAVNOH (Antifascist Council of the National Liberation of Croatia) on the creation of the Federal State of Croatia in 1945 were the foundations of present-day Croatia and that those values were defended in the 1990s war of independence.
Piskulic also condemned the downplaying of crimes committed in WWII by the Ustasha and the Chetniks.
Deputy Parliament Speaker Luka Bebic said the declaration on antifascism was an expression of the commitment to democracy, tolerance and solidarity and of the opposition to any form of extremism and radicalism. He advocated respecting all victims, both those killed in the Jasenovac death camp during WWII and the Croats killed towards the end of the war in Bleiburg field in Austria.
A telegram from PM Sanader was read out at the ceremony, which was also attended by members of parliament and government, representatives of political parties, the diplomatic corps, the judiciary, and others.
An exhibition was also staged at the concert hall with photographs of the Croatian antifascist movement from 1941-5, which may be seen until May 14.
Answering a question from the press afterwards about announcements that the definition of command responsibility would be changed and how this would affect the case of Ante Gotovina, the runaway general wanted by the Hague war crimes tribunal, President Mesic said, "We only want the truth to be established, and if that is conducive to the truth then I'll be satisfied".