At 0800 GMT the rand traded at 19.2350 against the U.S. dollar, about 0.3% weaker than its previous close.
The dollar index was little changed.
The rand initially strengthened after the finance minister's annual budget presentation on Wednesday, but the gains were short-lived.
The minister announced that the government would draw down 150 billion rand ($7.8 billion) from contingency reserves at the central bank over the next three years to limit rising debt, but he offered little in the way of broad structural reforms to fix problems such as high unemployment and stagnant economic growth.
"Once everyone has had a chance to dissect the data and assess it for what it is, it is not surprising to see the general reaction and narrative turn negative," ETM Analytics said in a research note.
The dollar, meanwhile, was supported by a senior U.S. Federal Reserve official saying that the Fed should be in no rush to reduce interest rates, which also contributed to the rand's weakness, ETM added.
South Africa has elections on May 29 in which the governing African National Congress (ANC) party is widely predicted to lose its parliamentary majority for the first time in 30 years, which analysts say has made some investors cautious.
On the stock market, the Top-40 index was up 0.37% in early trade.
The benchmark 2030 government bond was weaker in early deals, with the yield up 10 basis points at 10.105%.
(Reporting by Nellie Peyton; Editing by Alexander Winning and David Goodman)
