Many reserchers point ont that Korean Big Bishness Groups (Chaebols) have played very important part in development of Korean economy. And the other hand, it is true that Chaebols have made some serious problems, such as economic concentration. It is said that there are many Chaebols in Korea, but it is also widely believed that the biggest five Chaebols, such as Samsung, Hyundai, Lucky-Goldstar, Daewoo, and Sunkyung, have essentially made monopolistic condition in Korean economy.<br>The big Chaebols have created rapid growth from the early 1960's, through adapting to the industrial policy by government. And for rapid growth, close Chaebol-government relation and unrelated diversification are the best corporate strategies. In the developing period, which is characterized by a series of five-year plans and export-oriented industrialization, there was much cheaper labour force as competitive advantage But for the lack of industrial base formed historically and structually, there was few big companies. So the government was very positive to protect and bring up some big Chaebols through making several industrial policies. To make good use of such many business chances, some big Chaebols chose unrelated diversification in corporate strategy.<br>But from the end of 1980's, the ecomomic and political environment have been getting worse. It is true that the competitive advantage, such as cheaper labour force in 1960's and 1970's, have already disapperared, especially after the democratic reform in 1987. And because economic concentration has also been getting worse from the latter of 1980's, goverment has begun to regulate Chaebols' behavior and to intervene in the internal affairs in Chaebols.<br>So in corporate strategy, unrelated diversification has seemed to lose its effectiveness. In competitive advantage, high creative R & D will be very important To survive in severe competition, restructuring of diversified business is indispensable for the big Chaebols In corporate strategy, related diversification or vertical integration with high technological base will play an important part.