We empirically examine whether Korean domestic and foreign institutional investors influence corporate decision-making in the long and short run, and the decision-making in turn affects firm value and corporate performance. In general, institutional investors are considered to have information advantage and can perform a corporate monitoring role. We divide domestic and foreign institutional investors into the two types, i.e., long- and short-term investors in terms of the investment horizon. We also categorize corporate decision-making into long- and short-term decision-making by considering the time lag for which it has an effect on firm value or corporate performance Long- and short-term domestic and foreign institutional investors are defined using both trading data and insider ownership data. Long-term domestic and foreign institutional investors have a significantly positive effect on R&D investment, which is a long-term decision-making variable. By contrast, long-term institutional investors have a significantly negative effect on short-term decision-making, i.e., retained earnings or retention ratio. Domestic and foreign institutional investors seem to prefer long-term corporate decision-making by conducting investment activities for the purpose of portfolio diversification, and there was no significant difference in the impact on corporate decision-making between domestic and foreign institutional investors. We further look into the effect of corporate decision-making on firm value and corporate performance. R&D investment, which is a long-term corporate decision-making process, has a significantly positive effect on Tobin's Q, a proxy for long-term firm value. However, the retention ratio, proxy for the short-term decision-making, has a significantly negative effect on Tobin's Q. We can conclude that domestic and foreign institutional investors alike influence long- and short-term decision-making of Korean firms. In addition, it was found that the decision-making influenced by investors in turn can affect the long-term firm value and short-term performance of Korean firm. In particular, foreign institutions with long-term investment horizon significantly and positively affect firm value. So the study results imply that Korean firms should increase firm value by enhancing the corporate governance structure, and attract long-term foreign and domestic institutional investors.