Abstract This study explores relationships among structure,conduct and performance of Taiwan Financial Holding Companies by using SCP model of Industrial Organization theory. During the study period of 2004-2010,14 FHCs are examined by using fixed effect model and random effect model. Empirical results show that mergers and acquisitions (M&A) play a partial intermediation role between diversification and performance. Meanwhile,the results support the Behaviorist school who advocates that conduct is an intermediation which not only affect performance but also be effected by structure.