The event, organised by the Croat national community, is being held for the seventh time and this year the host city is Pecs, a town near the Croatian-Hungarian border, populated by a large number of Croats.
The event will also be attended by Hungarian President Laszlo Solym with whom Mesic is scheduled to hold talks.
The Days of Croats are organised by the Croatian State Self-Government and the Alliance of Croats in Hungary, an umbrella institution of the Croat national minority in Hungary.
It is estimated that some 90,000 Croats reside in Hungary. The two countries had signed an agreement on the mutual protection of minorities.