The 64-year-old former psychiatrist faces 11 counts of genocide, war crimes and crimes against humanity related to the 1992-95 Bosnian conflict, including the massacre of 7,000 Muslim men and boys in Srebrenica in 1995.
Karadzic's trial began Oct. 26, but he asked for more time to prepare his defense. The tribunal appointed him a lawyer, but Karadzic is instead working on his own with the counsel of Serbian legal advisor Goran Petronijevic, Radio B92 in Belgrade reported.
In the first of two days allotted to 3-hour opening statements, Karadzic reiterated his plea of innocence to charges of systematic ethnic cleansing.
"We will prove that there was no thought, much less a plan for getting rid of the Muslims," he said.
The prosecution is scheduled to call its first witnesses Wednesday, the report said.
Karadzic was arrested in Belgrade in July 2008. His military commander, Ratko Mladic remains a fugitive.