A study published by the local Stellenbosch University found that 99 of 139 samples contained species not declared in the product label.
This was mostly in sausages, burger patties and deli meats, it said.
The disclosure comes at a time of a growing scandal in Europe about horsemeat being sold as beef.
On Monday, Swiss company Ikea withdrew meatballs from sale in 14 European countries after tests in the Czech Republic found traces of horsemeat in a batch made in Sweden.
Leading supermarkets in the UK, including Tesco and Sainsbury, have also withdrawn beef products from shelves after they were found to contain horsemeat.
“There’s a fair share of fraudulent meat products on the South African market, according to a new study by meat scientists from Stellenbosch University,” the university reports on its news blog.
“The study found that anything from soya, donkey, goat and water buffalo were to be found in up to 68% of the 139 minced meats, burger patties, deli meats, sausages and dried meats that were tested. In other cases, even undeclared plant matter was detected.”
These ingredients were not declared on the products’ packaging labels, it said.
The study was done by experts from the Stellenbosch University’s Department of Animal Sciences and the Food & Allergy Consulting & Testing Services in Milnerton, Cape Town.
“Our study confirms that the mislabelling of processed meats is commonplace in South Africa and not only violates food labelling regulations, but also poses economic, religious, ethical and health impacts,” one of the researchers, Louwrens Hoffman, is quoted as saying.
The products tested were collected from retail outlets and butcheries, the university said.