The demonstrations took place in several major US cities, including New York, Boston, San Francisco, Chicago, Los Angeles and Seattle.
In New York, some 45,000 people reportedly turned out for the march which lasted two hours.
The protesters marched through downtown streets, holding anti-war signs and shouting ‘Get out of Iraq now’. The demonstrations brought together young and old, including grade school children, senior citizens and labour union activists.
In Chicago, thousands of protesters gathered at the Union Park and marched to the Federal Plaza. Organisers said anti-war rallies, sponsored nationally by a coalition of groups, headed by the United for Peace and Justice, also took place in Salt Lake City, Philadelphia, Orlando, New Orleans, Boston and Jonesborough in Tennessee.
In San Francisco, news reports said more than 10,000 people took part. Protesters along the Market Street dropped to the ground to honour the thousands of American troops and Iraqi citizens who have died in the war.