Peter Robinson has paid back £755 in parliamentary expenses claimed for a briefcase and computer case, it has emerged.
The DUP said he had bought “quality” items because they would be more robust and offer better value for money.
Mr Robinson said he had asked to be reimbursed only for the amount that would be paid for “standard” products.
However, the Commons authorities paid him the full amount and he has now paid back the whole claim.
A DUP spokesman said: “Peter was not required to make any repayment.
“He voluntarily decided to make the payment to the Fees Office, in spite of the fact that it was in relation to a legitimate claim which had been approved.”
SDLP leader Mark Durkan has paid back £1,124 to cover an overpaid electricity bill on a flat in London.
“I've received repayment of monies that I had previously claimed for so I've passed that repayment on to the Fees Office and the taxpayer,” he said.
In a statement the SDLP said: “In respect of the concerns over ‘redactions' or blackened-out details in the published expense forms, it should be made clear that Mr Durkan did not seek any of these.”
The party said he also repaid a £200 ‘cashback' offer he received from his mobile phone provider.
As revealed by the Belfast Telegraph last month, DUP MP David Simpson has returned £1,482, which relates to his second home in London.
Mr Simpson's office said the repayment was due to a mistake by the Commons in paying him twice for a month's mortgage interest relief payment.