Several hundred people demonstrated into the early hours of Wednesday outside the Palace of Justice in central Brussels, demanding the release of undocumented migrants, reported the dpa.
Police used force to break up an unlicensed protest on Tuesday outside the city's offices that deal with the registration of foreigners. They arrested 130 people.
The majority of those arrested were held overnight in the Palace of Justice, Belgian media reported.
The migrants face penalties for taking part in the unlicensed demonstration and they could also be deported, according to a spokesman for an organization that defends the rights of foreigners in Belgium.