8 July 1949
On July 1949,the Prohibition of Mixed Marriages Act, Act No 55 of 1949 that prohibited marriage or a sexual relationship between White people and people of other race groups in South Africa is passed. The law was introduced by the apartheid government and part of its overall policy of separateness. South Africans were required to register as members of one of four racial groups as set out in the Population Registration Act of 1950. The four groups were White, Coloured, Indian and Black. Using these categories, the apartheid government proceeded to criminalise marriages between people of different racial groups. Subsequent to the passing of this legislation, a number of people were arrested and charged for breaking its provisions. The law also nullified interracial marriages of South Africans that occurred outside of the country. It was eventually repealed in 1985 by the Immorality and Prohibition of Mixed Marriages Amendment Act that allowed inter-racial marriages and relationships.    
References

Beningfield, J.,(2006),  The Frightened Land: Land, Landscape and Politics in South Africa in the twentieth century, (New York), p.310|South End Museum Mixed Marriages Act, [online], Available at www.southendmuseum.co.za [Accessed: 04 July 2012]|African History, Apartheid Era Laws: Prohibition of Mixed Marriages Act No 55 of 1949, from About.com, [online], Available at https://africanhistory.about.com [Accessed: 04 July 2012]