The Korea Composite Stock Price Index tumbled as much as 2.1 percent in opening minutes, but then bounced back into positive territory briefly before slipping back. The benchmark index ended the session down 6.07 points, or 0.5 percent, at 1,279.85.
North Korea test-launched six missiles including a long-range Taepodong in an early morning barrage Wednesday, defying stern international warnings. The short-range missiles landed in the Sea of Japan. U.S. officials said the long-range Taepodong-2 failed shortly after take-off.
Comments by international ratings agencies Fitch Ratings and Moody's Investors Service on the outlook for South Korea's credit rating in the aftermath of the missile launches also helped the Kospi to trim losses, analysts said.
"Moody's comments which indicated it (the missile news) won't affect the country's ratings for now helped ease concerns," said Lee Gun-ung, an analyst at Daewoo Securities.
Moody's sovereign analyst Thomas Byrne said in an interview with Dow Jones Newswires that the positive outlook on South Korea's A3 government rating is not in jeopardy as long as North Korean risks are contained.
Among decliners, Hyundai Motor Co. fell 0.8 percent to 77,600 won and top lender Kookmin Bank lost 1.7 percent to 76,200 won.
Samsung Electronics Co., South Korea's largest coporation, rose 0.3 percent to 603,000 won, while steelmaker Posco gained 0,4 percent to 254,000 won.
Korea Electric Power Corp. also gained, rising 0.9 percent to 35,500 won.
Volume rose to 190 million shares worth U.S. $2.5 billion.
Decliners outnumbered gainers 541 to 202 with 69 stocks unchanged. One stock was up by its daily 15 percent limit, while one was limit down.
The South Korean won declined against the dollar for the first session in four. The dollar traded at 946.3 won, up from Tuesday's close of 943.4 won.