The Ethics Institute of South Africa said on Wednesday that ANC Deputy President Cyril Ramaphosa set an excellent example for other politicians to follow.
Ramaphosa resigned from company boards to avoid a conflict of interest.
On Wednesday, mining firm Lonmin and paper producer Mondi confirmed that he was stepping down as a director of both companies.
The institute's CEO Deon Roussouw said: "The moment you get decisive action and people setting the right tone, others in the vicinity start to follow. I think that's one of our biggest challenges in South Africa at the moment."