Mladic was ordered to leave the court after he repeatedly argued with the judge. He tried to speak several times at the beginning of the hearing, but the judge asked him to remain silent until he was allowed to speak.
The former general risks life in jail on charges of genocide, crimes against humanity and war crimes for his role in the bloody 1992-95 Bosnian war.
Mladic's court-appointed lawyer Alexandar Aleksic had asked the court to postpone the hearing because he had not been informed by his client that he would be present.
The lawyer on Sunday said his client told prison authorities he intended to boycott the hearing as his defence team had not been approved.
Mladic, aged-69, is being asked to plead to 11 counts related to his role in the bloody 1992-95 Bosnian war in which 100,000 people died.
The former military leader was arrested in Serbia in May and transferred to a UN detention unit in The Hague after 16 years on the run. His trial is not expected to start for months.