Rhino hunting is driven by soaring demand in newly affluent Asian countries such as Vietnam and China, where the animal's horns are prized as a key ingredient in traditional medicine.
Rhino horn has a street value of more than $65,000 (£39,000) a kilo in Asia, conservation groups say, making it more valuable than platinum, gold or cocaine.
The data is sure to ring conservation alarm bells about a downward population spiral in a country that is home to almost all of Africa and the world's rhinos, and it may bring renewed pressure on the government to do something to halt the killings.
In 2013, 1004 of the massive animals were illegally killed in South Africa, compared with 668 the previous year and 448 in 2011.
Most of the killings are taking place in South Africa's Kruger National Park.