Winfrey said the historically white University of the Free State had turned an ugly experience into a mode for confronting the challenges of reconciliation and remorse.
Four white students had made a video humiliating the black housekeeping staff. The students later apologized publicly, and the housekeepers accepted.
From the stage, Winfrey called the five cleaners heroes and the racial reconciliation nothing short of a miracle.
"It is truly what the new South Africa is all about," she said.
Winfrey said she had approached Jonathan Jansen, who in 2009 became the university's first black rector, after reading about his work, and accepted an invitation to come to speak to students.
A 4,500-seat auditorium was full for Winfrey's ceremony. Tickets were sold for 10 rand (about $1), most of that covering computer sales processing fees.
Winfrey is a frequent visitor to South Africa, where she opened a school in 2007 dedicated to giving bright young women of all races opportunities in a society where they are handicapped by conservative traditions as well as the poor schools that are a legacy of apartheid.
In a passage that drew cheers from the audience Friday, the citation accompanying Winfrey's honorary doctorate, the 152nd awarded by the university, said Winfrey "has truly become a South African.
"She did so because she believed that there was important work to be done here, and she wanted to be part of what Nelson Mandela and others had begun."
Previous recipients of Free State honorary degrees include anti-apartheid icons Mandela and Archbishop Desmond Tutu.
The Associated Press contributed to this report.