More than a million people have visited the grand two-storey house since it opened to the public in October 1967.
It hosts between 30,000 and 40,000 visitors a year.
The house, which has a 1276 sq m floor area and was designed by leading London architect Sir Ernest George, was given to the City of Dunedin by its previous owner, Dorothy Theomin.
She had died, aged 77, in October, 1966.
Don Barham, president of the Friends of Olveston, visited the house on Christmas Eve to mark the 120th anniversary of Miss Theomin's birth, on December 24, 1888.
Many of Olveston's more recent visitors have been overseas tourists.
Mr Barham hoped the economic downturn would encourage more New Zealanders, including more Dunedin residents, to visit Olveston, the former home of the Theomin family.
Miss Theomin had been a remarkable, public-spirited person, who had also been a keen golfer and mountaineer, he said.
As well as giving Olveston to Dunedin, she was also a strong supporter of the Dunedin Public Art Gallery, serving as president of the art gallery society.
Her father, a leading Dunedin businessman, David Theomin, had Olveston built, with the Theomin family taking up residence there in 1907.
