The National Assembly, acting in the absence of opposition members, voted yesterday to expel opposition leader Kim Young Sam.
The assembly ruled he had abused his position and privileges.
The United States said it regretted the move. President Carter met with Kim during his July visit to Seoul.
Most of the opposition members in the 235-seat house occupied the parliamentary building in an effort to block action against Kim, but 159 members of the ruling government party met in a conference room and provided the two-thirds majority vote necessary. One member of the ruling party was ill and did not attend.
Kim said the vote was "a [death] knell to democracy" in South Korea.
In Washington, State Department spokesman Hodding Carter said the United States "deeply regrets" the expulsion. "This action is inconsistent with the principles of democratic government," he said.
Sen. Edward M. Kennedy (D-Mass.) called the expulsion "blatantly inconsistent with democratic principles." He said it "should be strongly condemned by all supporters of Korean democracy."
The government party submitted a bill to censure Kim two weeks ago for telling the New York Times in an interview that the White House should end support for the government of President Park Chung Hee and that the presence of U.S. troops in South Korea amounted to interference in South Korean affairs.