A statement from the office of Serbian President Boris Tadic said Radovan Karadzic was located and arrested by Serbian security officers.
Mr Karadzic has been indicted for genocide over the 43-month siege of Sarajevo which claimed 12,000 lives and for orchestrating the 1995 massacre of some 8,000 Muslims at Srebrenica, the worst atrocity in Europe since World War Two.
He was brought to the investigative judge of the War Crimes Court in Belgrade, in accordance with the law on cooperation with the International Criminal Tribunal for the former Yugoslavia, the President said.
The prosecutor for the International Criminal Tribunal for the former Yugoslavia, Serge Brammertz, welcomed the arrest.
Mr Karadzic and his former military commander Ratko Mladic had been on the run from the ICTY for 13 years after they were charged with war crimes committed during Bosnia's 1992-1995 war. General Mladic is still at large.
