The balloon was donated to the gallery under the Cultural Gifts Program, which offers tax incentives to encourage people to donate cultural items to public art galleries, museums, libraries and archives in Australia.

Those who donate can claim the full market value of the gift, and the tax deduction can be spread over a period of up to five years.

The Canberra Times understands the balloon has been valued at $750,000.

The donation is currently being assessed by the Department of the Communication and the Arts.

The balloon was owned by Global Ballooning Australia. Founder Kiff Saunders has been contacted for comment.

Meanwhile the artist who created Skywhale, Patricia Piccinini, said she was "really excited" about the balloon becoming part of the national collection.

"For me, Skywhale belongs to the people of Australia but especially to the people of Canberra, so there is no better place for the work to be than the Australian National Gallery," Piccinini told The Canberra Times.

"They love the Skywhale and have the resources and the vision to insure that she lives on and can continue to contribute to the cultural life of the city.

"Canberra is where she belongs and so I couldn't be happier."

It's a long-awaited homecoming for Skywhale, which was commissioned by the ACT government to mark the centenary of Canberra in 2013.

It attracted much controversy over its unusual design and $300,000-plus pricetag.

The acquisition is part of a bigger plan for the gallery, which will be revealed in a month's time.

An earlier version of this story said a deduction of $250,000 could be claimed.