Twenty-three legislators of the national assembly on Tuesday said they have decided to quit from the ruling Uri Party to create a new party.
"With our deep regret and apology to the public, which is against the Uri Party, we are determined to give up our current power and become a seed to form a new united party," said legislator Lee.
Following the mass defection, the ruling party became the second-largest party in the national assembly with 110 seats while the conservative opposition Grand National Party takes the lead in the assembly with 127 seats.
According to local media, the defectors will form a negotiating group, which will be third largest in the parliament, before establishing a new party with other liberal forces, most likely members from the minor opposition Democratic Party.
The defection was widely regarded as a preparation for the presidential election this year. The ruling party has suffered from a low approving rate at only about 10 per cent.
The Uri Party was formed in November 2003 by former democracy activists and legislators loyal to Roh who defected from the Democratic Party, the ruling party then.