In order to enhance their performances, the mutual funds managers usually invest most of the funds on few potential stocks. Therefore, a large potion of these funds' total net assets value is in these potential stocks, in other words the investment concentration of these funds is relatively high. The purpose of this study is to explore the relationship between investment concentration and performance of funds. This study has three empirical findings. First, the higher investment concentration, the better performance is for the bull market. Secondly, the higher funds' turnover rate, the lower its investment concentration. Finally, the fund with higher total investment rate has higher investment concentration. The results imply that funds with higher investment concentration are more worthy to buy.