Minister Sussan Ley says she never intended to buy a Gold Coast unit when she set off for Queensland on a work trip with her husband in May 2015.
But the couple ended up doing a deal on a $795,000 unit, complete with views of Main Beach, in what her office suggested was a spur-of-the moment buy.
"The property purchase was not planned nor anticipated," a spokeswoman for the minister said in a statement on Friday.
The spokeswoman said Ms Ley and her husband had gone to the Gold Coast to meet with health stakeholders after addressing a media conference at a Brisbane hospital earlier in the day.
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There was nothing untoward about Ms Ley's partner being with her on the trip under "under family travel arrangements", she said.
"All travel undertaken was in accordance with the rules," the minister's spokeswoman said.
Deputy Prime Minister Barnaby Joyce defended the minister, saying there was no doubt she had travelled to Queensland on legitimate ministerial business.
He would not say if she'd displayed poor judgment by combining the work trip with personal business, saying that was a question for her.
But he told ABC television: "... if they made a purchase, even though I admit it is a substantial purchase, that's not the reason she went to the Gold Coast. She went to the Gold Coast for work".
But Opposition health spokeswoman Catherine King says Ms Ley owes taxpayers a better explanation.
"Sussan Ley needs to front up today and explain to Australians how purchasing a luxury apartment is considered to be official business," Ms King said in a statement.
"If she cannot do this, she has no choice but to resign, or Malcolm Turnbull must move her off his front bench.
"I don't know too many people who would spent that sort of money, even if they had it, on an impulse. It's a pretty unbelievable claim."
Former NSW Labor premier Kristina Keneally ridiculed the minister's explanation on Twitter, posting a picture of a bag of gummi bears with the message: "I mean, this bag of lollies is an 'unexpected purchase.' An investment property?
Ms Ley must reveal which stakeholders she met with on the Gold Coast, if a government car was used to facilitate the real estate deal, and how an opportunity to spontaneously buy property arose during a work trip, Ms King said.
Ms Ley's office has said she went to Brisbane's Wesley Hospital on Saturday, May 9, 2015 to announce new drugs being added to the Pharmaceutical Benefits Scheme.
On the Gold Coast later that day, she held meetings with "local health stakeholders, those being patients about access to new medicines", her office said.
