The Korea Composite Stock Price Index (KOSPI) closed down 0.87 percent at 1,990.33 points, ending a three-day winning streak.
"With global indexes generally treading water since the QE3 announcement, the lacklustre China PMI data served as downward pressure on markets today," said Lim Soo-kyun, an analyst at Samsung Securities.
"As for local factors, cyclicals such as tech, oil and chemicals weighed on the index due to falling oil prices and investors' profit-taking."
The HSBC flash PMI for China remained below 50 for the 11th month in a row, showing manufacturing in the world's second-largest economy was still contracting despite ticking up from a nine-month low in August.
Market heavyweight Samsung Electronics closed down 2.05 percent after trading nearly flat for the past three sessions.
Energy shares fell across the board, as oil refineries lost the most ground with SK Innovation sagging 4.3 percent and S-Oil slipping 3.2 percent.
Oil prices fell more than 3 percent on Wednesday on comments from top producer Saudi Arabia that it would take action to keep prices in check, as well as on US data showing crude stocks grew far more than expected.
Entertainment and leisure stocks were extremely bullish, with travel agency Hana Tour Service rallying 3.1 percent while movie theatre operator CJ CGV rose 3 percent.
"Many recent gainers in US and other global stock markets have been entertainment or smartphone-related firms, but in the South Korean market such companies are all mid- to small-caps and have less impact on the main board," said Lee Sun-yup, an analyst at Shinhan Investment Corp.