The university condemned the unidentified law professor, saying her use of blackface was "patently offensive" and "stupid."
"We condemn this action unequivocally as anathema to the University of Oregon’s cherished values of racial diversity and inclusion," the president and other UO leaders wrote in a campus-wide email.
"The use of blackface, even in jest at a Halloween party, is patently offensive and reinforces historically racist stereotypes," the email said. "It was a stupid act and is in no way defensible."
The university confirmed to BuzzFeed News that the professor was put on administrative leave pending an investigation into whether her actions violated university policy.
The professor has apologized for her decision and "has expressed concern about its potential impact on members of the community," the president's statement said. She also acknowledged that the "costume choice was unacceptable under any circumstances."