Johannesburg - There are an estimated 248 700 modern slaves in South Africa, according to the Global Slavery Index report released on Tuesday.
South Africa ranks in the top 50 in the index, in the 27th spot with Trinidad and Tobago.
The foundation examined practices such as forced labour, human trafficking, debt bondage, child exploitation and forced marriage.
The research in South Africa was conducted in 2015 using a random, nationally representative sample. It sought to identify instances of both forced marriage and forced labour within the general population.
About 103 461 victims of modern slavery in South Africa identified in the survey, were or are subjected to commercial sexual exploitation.
Although buying sex is illegal, the sex industry thrives on the street, in brothels and private homes.
South African women, together with women from neighbouring states, and Thai, Chinese, Russian and Brazilian women, were identified as likely victims of commercial sexual exploitation in South Africa.
South African women were also being trafficked abroad, predominantly to Europe.
Throughout 2015, the Hawks continued to identify Nigerian sex trafficking syndicates operating between the North West, Gauteng, and KwaZulu-Natal, according to the report.
The report revealed that 10 631 women were victims of forced marriage.
"Although Unicef data from 2015 reveals that South Africa has one of the lowest rates of child marriage in Sub-Saharan Africa, the persistence of some traditional practices have been noted by academics as fuelling early and forced marriages.”
More than 10 000 workers were subjected to forced labour in South Africa. Both women and children were employed as domestic workers.
"The legacy of apartheid, leaving many African and coloured women without education, has created a labour pool of unskilled workers who are funnelled into low-paying domestic work. Economic necessity is the key driver of women accepting work in the domestic service sector," the report stated.
Domestic workers in South Africa had reported employers withholding wages, unpaid overtime, and physical, sexual and psychological abuse.
While the Basic Conditions of Employment Act set the minimum age for employment at 15, young children were found to be working in agriculture, food services and street vending and were being forced to beg.
"Children in South Africa are trafficked from rural to urban areas, including to Bloemfontein, Cape Town, Durban, and Johannesburg," the report said.
There were an estimated 45.8 million people living in slavery globally. More than half of them, 58%, were in China, India, Pakistan, Bangladesh, and Uzbekistan.
Incidences of slavery were found in all 161 countries in the index. India had an estimated 18.4 million slaves among its population of 1.3 billion.
North Korea ranked highest on the scale, with one in every 20 people - or 4.4% of its 25 million population - in slavery.
The governments of North Korea, Iran, Eritrea, Equatorial Guinea and Hong Kong were doing the least to combat slavery.
The Netherlands, the United States, Britain, Sweden and Australia were the most proactive in combating it.