Abstract: The synergy effect of mergers and acquisitions(M&A) is able to enhance corporate value. China′s special institutional background and enterprise attributes are important special factors that affect the efficiency of M&A in China. The regional difference of legal protection of investor and the enterprise attribute difference will have different influence on synergy effect of M&A. By analyzing the M&A events of listed corporations occurred during 2007-2010, the paper finds that the effect of legal protection level of investor on M&A efficiency is different for firms with different ownership concentration: for companies with lower ownership concentration, the influence of the legal protection level of investor on M&A efficiency is closely related to enterprise attribute, and state-owned enterprises are more likely to have positive spillover effects, that is to say, the higher the legal protection level of investor the acquirer has, the more efficient the cross-regional M&A will be. On the contrary, private enterprises with lower level of legal protection are easy to trigger the “steward” spirit, and there is a significant “bootstrap” effect, that is to say, the corporate governance can be improved through the synergy gained by acquiring target enterprises with higher legal protection level of investor.

Key words: legal protection of investor, synergy effect, mergers and acquisitions, spillover effect, “bootstrap&rdquo, effect