Nuon Chea, 88, known as "Brother Number Two", and former head of state Khieu Samphan, 83, were given life sentences in August for crimes against humanity.
The pair were the first top figures to be jailed from a regime responsible for the deaths of up to two million Cambodians from 1975-1979.
Both men have lodged appeals against the convictions.
A second trial, in which they face genocide charges for the killings of ethnic Cham Muslims and Vietnamese as well as fresh counts of crimes against humanity and war crimes, began in July.
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The motion to disqualify the judges was dismissed earlier this month, and Nuon Chea's defence team returned to court last week.
But Khieu Samphan has continued to instruct his lawyers not to take part in proceedings, saying it would affect his "right to a fair trial".
The trial chamber Friday again ordered Khieu Samphan's defence team to resume the trial.
But after they still refused to attend the hearing today, judge Nil Nonn, president of the trial chamber, said the court had "no reasonable alternative but to adjourn the case".
The complex case against Nuon Chea and Khieu Samphan was split into a series of smaller trials in 2011 in a bid to get a faster verdict for reasons including their advanced age and the large number of accusations.
The August convictions followed a two-year trial focused on the forced evacuation of around two million Cambodians from Phnom Penh into rural labour camps, and on murders at one execution site.
Led by "Brother Number One" Pol Pot, who died in 1998 without ever facing justice, the Khmer Rouge dismantled modern society in Cambodia in their quest for an agrarian Marxist utopia.