Former Bosnian Serb leader Radovan Karadzic will go on trial at The Hague on Monday 26 October, the court says.
It is the second time in a week that the trial - originally due to start on 19 October - has been put back.
But Mr Karadzic's attempts to have the start delayed by 10 months have been rejected by the court.
Mr Karadzic is charged with 11 counts of war crimes and crimes against humanity, including genocide, dating back to the Bosnian war.
They include charges related to the 1995 massacre of about 8,000 men and boys at Srebrenica.
Mr Karadzic was arrested in Serbia and brought to the International Criminal Tribunal for the former Yugoslavia last year, after more than a decade in hiding.
The latest delay to the start date is to allow Mr Karadzic, who is defending himself, time to review new prosecution documents.
The court has called on the prosecution to present an updated indictment - or charge sheet - complete with prosecution notes, by 19 October.
The court has rejected Mr Karadzic's appeal that the case be dropped on the grounds that he was offered immunity from prosecution by former US mediator Richard Holbrooke in 1996 if he left public life.
Mr Holbrooke has repeatedly denied the claim.
The judges ruled on Tuesday: "Even if the alleged agreement were proved, it would not limit the jurisdiction of the tribunal, it would not otherwise be binding on the tribunal and it would not trigger the doctrine of abuse of process."