The Bank of Korea kept interest rates on hold at 2.25% at its latest policy meeting.
The BBC reports most economists had expected an interest rate rise to 2.5%.
The BoK previously held the rate at a record low 2% for 17 months in response to the economic downturn, before raising it to 2.25% in July.
The bank said it was not the right time to be raising the cost of borrowing. South Korea is Asia's fourth-largest economy.
The International Monetary Fund recently raised its 2010 growth forecast for South Korea's economy to 6.1% from 5.75%. But it also said that the rate of expansion would slow to 4.5% next year.