Abstract: With the rise of shareholder activism, institutional investors as big shareholders often choose to take the initiative to participate in corporate governance in order to standardize the organization structure and management behavior, so as to alleviate the agency conflicts, reduce agency cost, improve corporate governance efficiency. Obviously, whether China's institutional investors can play a positive role in reducing agency cost and increasing company value is becoming an important research topic. In this paper, the quarterly data of listed companies in Shanghai and Shenzhen stock Exchange is chosen as samples from 2007 to 2012. From the perspective of agency costs, stochastic frontier model is used to examine the impact of China's institutional investors on the company value. The analysis finds that with the increase of institutional investors holdings, the company value increased significantly, but it also shows an inverse-L-shaped relationship between the two. Based on this finding, panel threshold model is further adopted to search the threshold value over which the institutional investors' positive impact on company value shows a structural adjustment. The results find that when the proportion of institutional ownership exceeds about 12%, the impact of institutional investors on company value will be greatly diminished. Meanwhile, the evidence supporting the point of statement that open-end funds have more positive and significant influence on company value than closed-end funds is provided.

Key words: institutional investors, agency costs, stochastic frontier model, threshold regression