The benchmark Korea Composite Stock Price Index lost 6.44 points, or 0.27 percent, to 2,392.31 as of 11:20 a.m.
The Seoul index had opened higher on Wall Street gains. On Monday (local time), US stocks closed higher, with the Dow edging up 0.12 percent to its ninth-record closing high in a row and the S&P 500 adding 0.16 percent on consumer and technology sector gains.
Most large caps were mixed.
Tech shares were in positive terrain, with market kingpin Samsung Electronics adding 0.25 percent and SK hynix, a major chipmaker, jumping 2.03 percent.
Chem and insurance stocks were bearish. LG Chem, the country's top chemical firm, lost 1.02 percent, and No. 2 player Lotte Chemical decreased 2.16 percent.
The local currency was trading at 1,126.4 won against the US dollar, up 0.7 won from the previous session's close. (Yonhap)