The rupiah extended gains in afternoon trade as local shares jumped 1.4 percent, outpacing most Southeast Asian equity markets.
South Korea's won rose as much as 0.4 percent to 1045.6 per dollar, its strongest since Sept. 26, on demand from offshore funds and exporters. Seoul stocks rallied 1.8 percent to hit a three-week high.
The won pared some gains as President Park Geun-hye said she was concerned about the impact of a weaker yen on the local economy.
Some traders said they suspected the intervention of foreign exchange authorities in stemming the won's appreciation.
The Malaysian ringgit advanced as investors cut long-dollar positions.
The Fed is expected to announce the end of its bond-buying programme when it concludes a two-day policy meeting later on Wednesday. The US central bank is unlikely to flag a rise in interest rates soon due to slow global growth and low inflation.