The Korea Composite Stock Price Index (KOSPI) closed at 1,878.45, virtually unchanged from Friday's close of 1,878.87.
Foreigners were net sellers for an eighth straight session, offloading a net 344.9 billion won ($285.04 million) worth of shares on the main board, preliminary data showed.
The South Korean won gained modestly, supported by China's efforts to stabilise the yuan.
The local currency was quoted at 1,210.9 to the dollar at the conclusion of onshore trade, up 0.2 percent from the previous close of 1,213.4.