This is from BBB minus with money now set to become more expensive for the government to borrow.
The agency has cited political and institutional uncertainty, saying the country has a negative outlook.
Ratings agencies had warned South Africa that political risk could cause a downgrade to junk status.
S&p global has highlighted the executive changes initiated by President Jacob Zuma, saying these have put at risk - fiscal and growth outcomes.
It says a negative outlook reflects the view that political risks will remain elevated this year and that policy shifts are likely.
