The right-hand man to the late leader Khmer Rouge Pol Pot and a former Cambodian prime minister, 86-year-old Nuon is accused of murder and torture. He waived his right to be present in court on Friday because of health reasons, including heart disease.
"Notwithstanding the advanced age and frailty of the accused, Nuon Chea, and the accused's precarious physical health, the recent report and testimony of the court-appointed medical experts clearly indicate that the accused remains capable of meaningful participation in his own defense," Nil Nonn, president of the UN-backed court in Cambodia, said through an English translator.
Nuon is on trial alongside former Khmer Rouge head Khieu Samphan, 81, for war crimes and genocide charges. Among the charges the two face is the forced movement of people under a Khmer Rough policy to empty cities and the execution of as many as 3000 former military officers.
Nuon and Khieu both deny the charges.
Witness hearings against Nuon Khieu are to continue in the Extraordinary Chambers Court April 8.
Only one of five Khmer Rouge leaders indicted by the Cambodian court in 2007 has been convicted. Former prison chief Kaing Guek Eav was sentenced to life in prison.
Pol Pot died in 1998.