A call for the demonstration was launched on the social networking site facebook by a Basque youth organisation.
In all twelve coaches of demonstrators travelled all the way from the Basque Country to the Belgian capital.
The Basque protesters were joined by supporters of the Flemish nationalist party N-VA as well as other radical Flemish groups.
The protest was also aimed against intrusive police checks on students active in the Basque Movement.
There are allegations that many Basque students are being detained without great reason.