More than 20,000 people from nearly 40 countries paid their respects as wreaths were laid by the main monument to the victims of Nazism.
The Croatian delegation was headed by Deputy Parliament Speaker Mato Arlovic and included representatives of the Croatian Embassy in Austria, Homeland War veterans and volunteers, and the Alliance of Antifascist Fighters and Antifascists.
"We have gathered to pay tribute to the victims of Nazism and show that suffering must not be forgotten. Antifascism is a universal and obligatory element of every democracy and it is embedded into Croatia's foundations," Arlovic said after laying wreaths by a memorial plaque Croatia set up in 2001.
Arlovic said that the memories of last decade's war of independence were still fresh in Croatia and that it was therefore "understandable that Croatia and all the factors in its political life are determined in condemning all forms of extremism, racism, intolerance, radicalism and nationalism, regardless of its sources and promoters".
The Mauthausen death camp was established in 1938. About 200,000 people were detained there over the seven years of its existence, of whom half were killed. US forces liberated the camp on 5 May 1945.