The court in Salzburg decided to extend Sanader's detention because he was regarded as a flight risk, the spokeswoman said.
The court postponed Sanader's extradition to Croatia where he is wanted on corruption charges.
The former Croatian premier was arrested in Austria on 10 December on an international warrant issued by Croatia which suspects him of abuse of office and involvement in a joint criminal enterprise.
Sanader has refused to be handed over to the Croatian authorities, explaining that his lawyers have not yet seen his case file and that his apprehension and prosecution are politically motivated.