This study investigates the effect of board networks on M&A transactions. I select 331 samples of M&A transactions among U.S. Fortunate 500 companies which are also U.S. public companies from 2002 to 2011. In addition, I use definition of board networks by Cai & Sevilir (2012) to identify whether there exist board networks in each sample. About research design, first I use event study methodology to estimates cumulative abnormal returns (CAR), and then examine the relationship between the board networks and M&A performance through regression analysis. Empirical analysis results are as follows:¡G 1. M&A announcement brings significantly negative abnormal returns to the U.S. Fortunate 500 companies. 2. The board networks will decrease the M&A performance for the U.S. Fortunate 500 companies. 3. The board networks are not efficient information channels for the U.S. Fortunate 500 companies.