SEOUL—South Korean lawmakers voted Tuesday to move half of the national government to a city being built about 100 kilometers south of Seoul, rejecting President Lee Myung-bak's effort to keep the government together.

The lawmakers voted 164-to-105 against Mr. Lee's bill to modify plans for the city, being paid for with $20 billion in taxpayer funds, to become a center of science and manufacturing rather than an administrative center.

As...