This paper studies the relationship between market competition and media performance in Taiwan. A close examination of the existing literature reveals that no conclusive findings have been published; some studies discovered positive relationships and others discovered contradictory ones. Using content diversity of TV programmes to represent media performance, this study analyzed the diversity among primetime series ran by the three TV stations in Taiwan. Three indicators were employed to measure diversity: duration of series, diversity of vertical programming, and the numbers of actors. F or more than 20 years the TV market in Taiwan was under rigid regulation, with only three stations dominating the market. But recently, with the satellite TV industry prospering in the Asia-Pacific region, Taiwan began to feel the impact of globalization, and the situation has undergone a major transformation.