Members of the so-called coloured population are incarcerated at a rate almost double that of their black compatriots, says the SA Institute of Race Relations (SAIRR).
Evidence suggested the higher prison rate could be attributed to the prevalence of gangsterism, alcohol and drug abuse among this group, the institute said in a statement on Tuesday.
"In October 2007, some 80 percent of the South African prison population was made up of Africans, who also made up 79 percent of the entire South African population.
"However, the coloured population was incarcerated at a rate of almost 651 per 100 000 people. This was almost twice the imprisonment rate of the African population, which was 342 per 100 000 people in 2007.
"White and Indian populations were incarcerated at the same rate of around 60 per 100 000 people."