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The local currency was quoted at 1,116.4 against the dollar at 0025 GMT, compared to Wednesday's domestic close at 1,114.6.
The Bank of Korea's monetary policy committee will probably cut interest rates by 25 basis points to 2.75 percent to support the flagging economy, a survey of 24 analysts by Reuters found.
The central bank will also release revised growth and inflation forecasts for 2012 and 2013 later in the day.
The benchmark Korea Composite Stock Price Index was down 0.4 percent.
Local bonds were off to a robust start with investors largely convinced the central bank will cut rates. December futures on three-year treasury bonds were up 0.07 points to trade at 106.60.