American forces entered the camp on 11 April 1945, bringing an end to the ordeal of 21,000 prisoners being held there by Nazi troops.
Former inmates and war veterans returned to the site, near the German city of Weimar to mark the anniversary.
It was the first major camp to be liberated by the Americans at the end of World War II.
Survivor Henry Oster said his memories of Buchenwald would last "forever".
"When someone asks how Buchenwald was, you immediately see the dead bodies again," he told AP.
More than 250,000 men, women and children were held at Buchenwald from its opening in 1937 until its closure eight years later. About 56,000 people, including Jews, Roma and Soviet prisoners, died within its walls.
Crowds laid flowers at a memorial for the victims on Saturday and held a minute's silence at 15:15 - the time US troops entered the site.
Mr Oster, 86, recalled the day the soldiers arrived to free prisoners.
"We had no idea the Allies were in Europe. When we heard noises at about 15:30, we looked out of the window, which took a great effort," he said.
"One of my friends said with a weak voice, 'I think we are getting liberated'. We thought he had lost his sense of reality like so many people there."
Mr Oster, a German Jew from Cologne, was taken to an orphanage in France and emigrated to the United States in 1946.
Former army medic James Anderson, 91, also attended the commemoration ceremony.
"The devastation was so tremendous," he said. "The prisoners were so glad to see us, they would hug us and everything.''

Strathbungo residents are being asked to take part in Window Wanderland at 18:00-21:00 on Saturday 25 February.
Artist Lucy Reeves, who ran her first event in Bristol in 2015, said it helped bring out people's playful side.
Previous events have seen windows with paper silhouettes, laser projections and people staging performances.
The event aims to encourage people to come outdoors for an evening walk around the neighbourhood.
Ms Reeves said: "I wanted to make an event that anyone can participate in, is easy to do, and creates something different.
"This brightens up the long winter nights giving everyone a great excuse to get outdoors.
"We have had displays made by schools, grandparents, even pets, some are silly, some are serious.
"It is a proper community event, some roads had almost every house participating, using campervans, top floor windows and even decorating hedges with lights."
Residents are being encouraged to sign up on the event's Facebook page or website.
Following the Bristol trail, seven areas in the UK ran an event in 2016, with a further 11 planned this year.

Sir Philip Bailhache, then Jersey's attorney general, supervised Roger Holland's appointment to the honorary police in 1992.
Holland had been convicted of sexually assaulting a 14-year-old girl with learning difficulties in 1986, when he worked for St John Ambulance.
Sir Philip said he had not known before Holland's inauguration.
Holland was jailed for two years in 2008 for eight sexual offences, some of which were committed while he was in the honorary force.
Despite including the 1986 conviction on his application form, he was elected to the St Helier honorary police in 1992, where he held office for another six years.
Sir Philip said he was only informed of Holland's conviction after the election, and "it was reasonable to conclude he had been re-habilitated".
"What Holland did was put his hand up a girl's pullover. It was an unpleasant thing to do but across the range of sexual offences it was at the lower end of the scale.", he said.
The Jersey Care Inquiry is investigating allegations of child abuse in Jersey's care system since 1945.
Sir Philip, Jersey's current external relations minister, also denied he deliberately distracted attention from abuse victims in a speech he gave in 2008.
He told people on Liberation Day :"All child abuse is scandalous but it is the unjustified and remorseless denigration of Jersey and her people that is the real scandal."
Sir Philip told the inquiry he was not "diminishing the gravity of child abuse" but that his choice of words were possibly "unfortunate".
Survivors have returned to the Buchenwald concentration camp 70 years after it was liberated by US soldiers.
[NEXT_CONCEPT]
A Glasgow neighbourhood is being encouraged to create a window display in their home to help turn the area into an outdoor evening gallery.
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A former senior judge was "not aware" a man was a convicted sex offender when he was admitted to a voluntary police force, an inquiry has heard.