Protesters shouted chants of "red trash" and "resignation," criticizing the newly elected prime minister's cabinet appointments, the news website Novonite.com reported.
Opponents of Oresharski, who was appointed prime minister by Parliament May 29, have called for the introduction of more transparent practices in politics, the news website said.
Demonstrators held signs in the midst of a heavy summer storm in Sofia that read "this is a protest against impudence," "forgiveness, no thanks," "today we create New Bulgaria -- with new Parliament and Bulgarian politics" and "Bulgarian police worthy for respect," Focus news agency reported.
Some Bulgarian citizens have said the country's election system needs an overhaul so that it is a more adequate representation of the people's will, Novonite.com said.
Britney Spears debuts 'Perfume' video
Wisconsin business offering 'therapeutic cuddling' forced to close