At 0635 GMT, the rand traded at 15.4850 against the U.S. dollar, 0.6% weaker than its close on Monday.
The unit had climbed to 15.2100 per dollar on Monday, its strongest since March 5, as markets went into a frenzy on drugmaker Pfizer's announcement that its trial vaccine has been highly effective in preventing COVID-19.
"A move back to 15.50 will likely see further supply from exporters, but should we start to see sustained position covering from offshore entities, I can easily see a quickfire move back to 15.85/16.00 due to lack of liquidity and weak short positions," Warrick Butler, chief trader at Standard Bank, said in a note.
Government bonds also weakened in early trade, with the yield on the benchmark instrument due in 2030 adding 18.5 basis points to 8.915%.
(Reporting by Olivia Kumwenda-Mtambo; editing by Uttaresh.V)