The provisional release followed April 14 decisions reached by the tribunal's Trial Chamber III, the UN court said in a press release.
The execution of the decisions on the provisional release of Milutinovic, Sainovic and Ojdanic had been postponed for 24 hours at the Prosecution's request, which expected possible appeals against the decisions.
Following the Prosecution's subsequent decision not to file any appeals, arrangements were put in place for the swift provisional release of all four accused.
The four accused had been escorted to Belgrade by Serbian Administration Minister Zoran Loncar.