South Korea's parliament has approved a government plan to bring home 1,000 of its 3,200 troops stationed in Iraq.
The National Assembly backed the measure by 110-31, but extended the remaining troops' mission by a year.
South Korea's contingent of troops is the largest in Iraq after those of allies the US and Britain.
The proposed withdrawal came to light during a visit to South Korea by US President George W Bush, and caught the White House by surprise.
The South Korean public is sharply divided over the issue of the deployment of its troops in Iraq.
The troops were sent partly to underpin the close military alliance between Washington and South Korea, which relies on US forces to defend against possible attack by North Korea.
But many South Koreans are questioning whether that threat still remains, and whether the relationship therefore needs to change.
The South Korean troops are stationed in the Kurdish-controlled town of Irbil, in northern Iraq.
Analysts say that while Irbil's security situation is much better than Baghdad's, it has still suffered periodic violence.