The centre of the city was sealed off as marching soldier and elaborate floats celebrated the day in 1975 when tanks smashed through the gates of the Presidential Palace in what is now Ho Chi Minh City, ending a bloody and protracted war with the US.
No American official attended the anniversary parade, but the US Ambassador will attend a small ceremony at the city's consulate.
"The April 30 victory was a golden turning point for the Vietnamese people," Army Lieutenant-General Nguyen Quoc Khanh told the crowds at the event.
The victory is a symbol of the country's hard-won independence, he said, adding that the army "is ready to sacrifice" anything to defend this.
The Northern victors reunited the country under a communist government after a war which eviscerated much of Vietnam, killing millions of its people as well as 58,000 American servicemen.
