Both Korea and Japan are leading exporting countries of advanced manufactured products, and the competitive and efficient manufacturing activities are important pillars of the affluence of the two economies. Yet, comparing the manufacturing sectors of the two countries in the 1990s brings to light a startling contrast in their performance. Applying the same empirical method to the analysis of micro-data for Japanese manufacturing firms for 1994-2001 and Korean manufacturing plants for 1990-98, this paper examines differentials in Japanese and Korean productivity growth. This paper focuses on the role of competition in firm dynamics and on the importance of internationalization as a major determinant of firm performance.