The organizers urged participants to carry red cards as a way of showing "a red card to politicians and institutions facilitating war crimes against Palestinians."
"Although the federal government finally decided to take measures against Israel on September 2, these measures still fall far short of all Belgium's international obligations," said Ludo De Brabander, one of the organizers.
He added that Belgium must take "decisive and comprehensive measures" to end its complicity in the genocide.
Demonstrators demanded a full military embargo on Israel, including an end to arms trade and cooperation, as well as a national ban on investments, trade, and diplomatic relations that could contribute to the occupation of Palestinian territories.
The rally, organized by international solidarity groups, was supported by over 200 organizations, including trade unions, Jewish and Palestinian groups, youth movements, religious organizations, cultural associations, and charities.
The first "Red Line" march on July 15 drew around 100,000 participants.
Israel's genocidal war in Gaza marked its 700th day on Friday, with Israel having killed over 64,000 Palestinians. The military campaign has devastated the enclave, which is facing famine.
Last November, the International Criminal Court issued arrest warrants for Israeli Prime Minister Benjamin Netanyahu and his former Defense Minister Yoav Gallant for war crimes and crimes against humanity in Gaza.
Israel also faces a genocide case at the International Court of Justice for its war on the enclave.
