Mihajlovic testified about relations between political leaders of the former Federal Republic of Yugoslavia (FRY), which comprised Serbia and Montenegro, and the Bosnian Serb entity from 1993 to 1997, when his party "New Democracy" was a coalition partner in the Serbian government led by Slobodan Milosevic's Socialist Party.
The ICJ has imposed an embargo on the media reporting about the content of testimonies until the last witness testifies on March 28.
Later in the day the witness stand will be taken by Vladimir Milicevic, who headed the department for foreign nationals in the police department of the Serbian town of Krusevac in the summer of 1995, when the Bosnian Serb army allegedly committed genocide in the eastern Bosnian town of Srebrenica.
Milicevic's testimony will focus on the treatment of Bosnian Muslim refugees by the then FRY authorities and the reception of women and children from Srebrenica in Krusevac in July 1995.
Serbia and Montenegro has so far called six of the seven witnesses and expert witnesses.
The presentation of evidence ends on Tuesday.
The prosecution has introduced two witnesses so far.
The trial in the case that was launched in March 1993 will end with a second round of presentation of arguments by the two sides, to last from 18 April to May 9.
The ICJ will be deliberating the case for several months before it reaches a verdict in its first case dealing with violations of the UN Convention on Genocide.