This research examines the effect of institutional ownership, independent board and the board size to firm performance. Using fixed effect data panel regression, this research investigates 293 firms listed in the Indonesian Stock Exchange during 2010-2015. Firm performance is proxied by market measure (To-bin’s Q). The findings of this research suggest that the institutional ownership, the board of Independence has a positive impact only to Tobin’s Q value, while the board size can increase both Tobin’s Q. This research also finds that the board size has a non-linear relationship with investment as proxied by IOS. While the IOS variables can mediate the effect of board size on firm performance.