Stellenbosch University condemned "racial superiority and any attempts to polarise" the campus, a spokesman said.
The posters, reminiscent of Nazi propaganda to rally support for Hitler, called for a "Fight for Stellenbosch".
The university has been fraught with racial tension since white minority rule ended in 1994.
Before the end of apartheid, it was an elite institution for Afrikaans-speaking white people.
The university, now open to all races, has been hit by protests over language policy, tuition fees, and alleged racism.
In 2015, the university's governing body voted to retain Afrikaans as the main language of instruction, rejecting calls for it to be replaced by English.
Most black people in South Africa prefer to speak English than Afrikaans.
The posters were issued in the name of "The New Right", and called on "Anglo-Afrikaner" students to attend a meeting on Thursday to "Fight for Stellenbosch".
It is not clear who is behind the posters
The images were a recreation of the Nazi-era League of German Girls, and of slogans such as "The German student fighting for the Fuhrer and the people".
The posters have caused outrage, with people saying they were the latest example of racism and inequality at the prestigious institution, says the BBC's Pumza Fihlani in the main city, Johannesburg.
In a statement, the university said the posters were "totally unacceptable" and it was still unclear who was behind them.
"There seems to be deliberate mischief-making involved, and if that should be the case, disciplinary steps will be taken," Vice-Chancellor Wim de Villiers said.