By Kate McGeown
BBC News, Manila
The appointment gives Mrs Arroyo another ally in the Supreme Court
A row is brewing in the Philippines between the outgoing president, Gloria Macapagal Arroyo, and the man set to become her successor, Benigno Aquino.
Mrs Arroyo has sworn in a new Supreme Court Chief Justice, whose appointment has been questioned by Mr Aquino.
Mr Aquino has questioned whether she can make such an important decision so close to the end of her term.
He has even hinted he might refuse to take his oath of office in front Chief Justice Renato Corona.
Mr Corona will only have about six weeks in his post under the presidency of Gloria Arroyo.
The new president will take over at the end of June, and unofficial results from last week's election show that Mr Aquino, more commonly known as Noynoy, won an easy victory.
Mr Aquino has made no secret of the fact he disproves of Mr Corona's appointment.
But the row is about more than just one appointment.
Mr Aquino's main campaign pledge was to stamp out corruption, and that includes looking into allegations involving Mrs Arroyo.
The former president will still wield a lot of influence when she steps down.
She has a seat in Congress, and many allies in the Supreme Court - now including Mr Corona.