Over £700,000 of public money has been spent on the Commons Speaker's official residence since 2001, figures show.
A Freedom of Information request by the Daily Telegraph revealed that over £100,000 a year was spent on furniture, art and air-conditioning.
Speaker Michael Martin's spokeswoman said the improvements were necessary.
Mr Martin has been criticised after his family used air miles from official flights, and his wife claimed cab fares for shopping trips.
The figures show that £148,900 has been spent on furniture, £13,000 on art, £191,000 on installing a new air-conditioning system, and £291,000 on "building restoration and refurbishment".
A further £992,000 has been spent on the Speaker's garden - although most of those costs are part of the effort to improve security in the Palace of Westminster since the 11 September 2001 attacks.
Former independent MP Martin Bell said he was "shocked" by the sums involved.
"The Speaker should be setting a good example and he is not - MPs have got to get their palace in order," he said.
Mark Wallace, campaign director of the TaxPayers' Alliance, said the figures were "stupendous".
"The Speaker is well paid and receives generous allowances as well as a free house, so it is excessive for him to be billing so heavily for furniture, art and cooling systems."
The revelations come as Michael Martin carries out a review into MPs' expenses, due to report in the autumn.
But his own expenses have been the subject of scrutiny and his spokesman, Mike Granatt, resigned in February after he wrongly rebutted some parts of a story claiming that the Speaker's wife had claimed more than £4,000 in taxi expenses since May 2004.
Mr Martin's spokeswoman said the spending on Speaker's House was part of a rolling programme of improvements.
She added that the property was used for entertaining heads of state and needed to be maintained as part of Britain's heritage.
"Speaker's House is the official residence of the Speaker," she said.
"Entertainment of visiting heads of state, parliamentarians and others take place in the State Apartments and the costs listed reflect environmental and heritage requirements and health and safety legislation."