Recently, a question arises how interest rate differential affects the exchange rate over the capital inflow on stock and vice versa. As a matter of fact, the Korean policy interest rate has been higher than that of the United States. while the United States interest rate is, sometimes, higher than that of Korea. Especially, in these days. the United States policy interest rate has been lowered down due to the subprime mortgage problems and the interest rate differential has been widened. Consequently, a serious concern about its effect on the Won/Dollar exchange rate has been arisen in the 4th quarter of 2008. In this respect, this paper would like to find out the empirical correlation study of interest rate differential and exchange rate between the United States and Korea in Chapter I, and study the theoretical and precedent research works in Chapter II, International Comprison of Interest Differential and Exchange Rate in Chapter III, Correlation of Interest Differential and exchange Rate in Chapter IV, Correlation of BIS Capital Adequacy Ratio, Stock Index, and Exchange Rate: International Comparison in Chapter V, Concluding Remarks: Toward Optimal Exchange Monitoring System in Chapter VI.