At 0927 GMT, the rand traded at 18.6400 against the dollar, about 1% weaker than its closing level on Friday.
The dollar was up around 0.2% against a basket of global currencies.
Casey Delport, an investment analyst at Anchor Capital, said it was difficult to pinpoint exactly what had caused markets to shift to a risk-off footing, but that while that persisted the rand would be on the defensive.
She said one factor was recent economic data out of the United States which had made some traders speculate that the Federal Reserve will raise interest rates again in September.
A major focus for markets this week will be inflation data out of China, Germany and the United States.
"This data can recalibrate the market's outlook on monetary policy once again, which will feed directly into currency prices, thus a cautious start to the week is envisaged," Rand Merchant Bank analysts said in a research note.
On Monday, South Africa will hold its weekly Treasury-bill auction, while central bank data showed the country's net foreign reserves rose in July to $55.626 billion.
The Johannesburg Stock Exchange's blue-chip Top 40 index was little changed. South Africa's benchmark 2030 government bond was slightly weaker, with the yield up 5.5 basis points to 10.315%.
(Reporting by Tannur AndersEditing by Alexander Winning and Sharon Singleton)
