The rand was trading at 7.5215 to the dollar at 0651 GMT, 0.33 percent firmer than Monday's New York close of 7.55.

The US Fed policy announcement will be watched closely by traders for any signals of further quantitative easing, but the Fed is unlikely offer any hints on new stimulus on the back of positive economic data already seen.

"The rand is slightly stronger on the day, basically on the back of better commodity prices, a little bit of support on the equity space," said Brigid Taylor, Head of Institutional Sales at Nedbank.

"It looks as though the global growth outlook is starting to improve slightly and therefore data is quite important, it seems unlikely that we will see QE3 which will keep the rand range bound," she said.

The National Treasury is due to hold its auction at 0900 GMT, offering 2.1 billion rand worth of its 2017, 2021 and 2036 bonds.

Yields on both the two main benchmark government bonds were down two basis points, with the 2015 yield at 6.66 percent and that on the 2026 note at 8.28 percent.

Stocks opened higher, with the JSE's blue-chip Top-40 up 0.53 percent shortly after the 0700 GMT start of trade.