The event was attended by several hundred people, including Croatian President Stjepan Mesic.
The first partisan unit, consisting mostly of Croats from Sisak, antifascists and communists, was set up in Brezovica on 22 June 1941.
President Mesic said at the commemoration that the establishment of the unit had been a turning point in Croatia's history and that it had laid the cornerstone of today's Croatia.
The antifascist struggle saved the honour of the Croatian people at a time when there were Croats who were willing to implement the policy of the occupying forces and side with terror, Mesic said.
The uprising which started in Brezovica resulted in the largest free territory in the occupied Europe and it was headed by Josip Broz, a Croat who will be remembered as Tito, Mesic said.
He went on to say that attempts to revise World War II in Croatia in the past 15 years would not be tolerated.
"The truth is that the antifascist movement was headed by communists, but most antifascists were not communists. The truth is that a large number of Croatian Serbs took part in the struggle for Croatia's liberation, but that fight was not fought only by Serbs, nor was it a fight against Croatia. The ethnic composition of the Sisak unit is the best proof of that".
Germans, Italians, the Czech and other minorities, and even members of enemy units who joined the People's Liberation Army, took part in that struggle, Mesic said.
"Things that should not have been tolerated happened on the side of the winner too. Crimes were committed, which is not good, but unlike Nazism and fascism, whose ideology and implementation was based on crime, the idea of anti-fascism was pure."
Mesic went on to say that everything had its historical context, including the concentration camp Jasenovac, where he said people had been systematically killed only because of their ethnic background or opposition to the regime.
"Bleiburg too has its own historical context, with the Allies having handed over to partisans a large and diverse group of soldiers and civilians, including Croats, Serbs, Montenegrins, Slovenes, Ustasha, members of the Home Guard, Chetniks and members of the White Guard... although many of them deserved punishment, what happened later at Bleiburg cannot be approved, but it also should not be falsified."
"Liquidation without trial is absolutely unacceptable... it was the revenge of the winner against the enemy who would not admit defeat and surrender," the President said among other things.
The celebration in Brezovica, held under President Mesic's auspices, was organised by the Sisak County authorities and the Federation of Antifascists and Antifascist Fighters of Croatia. The event was attended by antifascists from Croatia, delegations of state institutions, the parliament and the government, representatives of political parties, the Jewish community, the Serb minority, and foreign embassies, as well as by partisans from Italy and antifascists from Slovenia and Bosnia-Herzegovina.