Mladic is wanted by the Hague Tribunal on genocide and war crimes charges. The charges include his alleged responsibility for the 1995 massacre of at least 7,500 Muslim men and boys from the town of Srebrenica. It was Europe's worst slaughter since World War II.
Tadic declined to give details of the arrest operation, saying only that he was arrested on Serbian soil. He said that information will be made public following an investigation by security services.
Serbia, which strives for the European Union (EU) membership, hopes his arrest would help put the its pariah state status behind. "I believe all the doors for our membership in the EU have been opened now," Tadic said.
Having lived freely in Belgrade for some time, Mladic disappeared from view when former Yugoslav President Slobodan Milosevic was arrested in 2001.
Serbia has been accused of not acting aggressively enough to apprehend Mladic who is suspected of being harboured by elements of the military and perhaps government.
The country will try to use the arrest as evidence that it stands on the side of justice and not the nationalism that fuelled the war in the former Yugoslavia.
"Nobody should doubt now or ever that Serbia cooperates with the Hague," Tadic said.
Serbian-Croat Goran Hadzic remains at large with a Hague arrest warrant for suspected war crimes against him. Tadic pledged to bring him to justice."Goran will be arrested. I promise you it will happen," he said.
