Namibia, Seychelles and Swaziland also improved their scores
South Africa moved up eight places to 43rd in Transparency International's annual Corruption Perception Index.
The country tied with Malaysia and South Korea with a score of 5,1 - barely a pass mark on a scale where 10 is completely clean and 0 highly corrupt.
South Africa came second to Botswana as the least corrupt African country. Botswana was rated 38th cleanest out of the 180 countries surveyed.
New Zealand, Denmark and Finland tied with 9,4 as the least corrupt countries, followed by 9,3 for Singapore and Sweden.
The index showed a correlation between a country's wealth and honesty. Poorer countries have the highest levels of corruption.
At the bottom end of the scale, Somalia and Myanmar tied as most corrupt countries with 1,4 points. Zimbabwe was rated 150 with 2,1 points, behind Nigeria's 147th rank with 2,2.
Namibia, Seychelles and Swaziland improved their scores. "These results reflect the positive progress of anti-corruption efforts in Africa and show that a genuine political will and reform can lower perceived levels of corruption," the report said.
"Despite some gains, corruption remains an enormous drain on resources needed for education, health and infrastructure," said Transparency International chairperson Huguette Labelle.
"Low scoring countries need to take these results seriously and act now to strengthen accountability in public institutions," she said.
More information can be found at www.transparency.org.