People cheered and waved flags under sunny skies as entertainers performed and the world-famous Snowbirds acrobatic flying team roared over the Peace Tower, the Canadian Broadcasting Corp. reported.
There were children with their faces painted with the maple leaf, the national symbol. Veterans showed off their military medals.
The festivities began with a Canada Day parade through the streets of Ottawa, ending at the Supreme Court of Canada building.
Among those joining the celebrations were Canadian Governor General Adrienne Clarkson and Prime Minister Paul Martin, fresh from his recent election victory.
"Our pride in our cultural diversity and the richness it brings to our society is second to no other," Martin told the cheering crowd. "Canada is second to no other."