As a number of studies in macroeconomics attempt to explain the business cycle and asset pricing using firm dynamics, there is a growing interest in understanding how firms make financing decisions about the use of debt and equity in varying stages of the business cycle. Most of the studies, however, have overlooked the possibility that the cyclical behavior of equity issuance is different from that of debt issuance. They focus mainly on the procyclicality of debt financing or external financing in total. Similarly, little work has been done in corporate finance literature also on the cyclicality of firms' financing behavior. The main concern there is to control macroeconomic factors in testing the traditional capital structure theories. Because the business cycle changes the amounts of debt and equity to be raised, which in turn influences the business cycle through corporate investments, it is meaningful to look into the cyclicality of debt and equity financings. Previous studies reveal conflicting views on the cyclicality of debt and equity financings. Using the NBER Business Cycle Data, Choe, Masulis, and Nanda (1993) find that the amount of equity raised is larger in expansion periods than in contraction periods, whereas the opposite is true for the amount of debt raised. However, because they only analyze a subset of external financing vehicles such as common stocks and corporate bonds, they fail to control the influences of large firms with relatively easy access to financial markets. Korajczyk and Levy (2003) document that the debt-equity ratio increases during recessions. But the use of the debt-equity ratio implicitly assumes that debt and equity financings are substitutes for each other, and thus rules out the possibility that they show the same cyclical behavior. Moreover, the macroeconomic variables used by Korajczyk and Levy (2003), such as equity market returns and term spreads, are not the typical measures of cyclicality in macroeconomics literature. While the two aforementioned studies argue that equity issuance is procyclical and debt issuance is countercyclical, Jermann and Quadrini (2012) claim that equity financing is countercyclical and debt financing is procyclical. They use the flow of funds data from the Federal Reserve Board. But their dataset does not include all of corporate debt and equity transactions, and thus it is strongly influenced by a small number of large firms and by the procyclicality of mergers (Baker and Wurgler, 2002). To overcome the limitations of the preceding studies, Covas and Den Haan (2011) divide firms into several groups by size and investigate the cyclicality of small firms' financing behavior separately. They also construct a comprehensive time-series dataset of debt and equity issuances using the accounting data for individual firms in Compustat, instead of using the aggregate data that may cause a biased result due to the effect of large firms. Moreover, as with other studies in business cycle literature, they filter the real GDP or the value added by the Hodrick-Prescott (HP) method and use it as a measure for real activity. Unlike the results of the preceding studies, their finding is that both debt and equity financings are procyclical. Regarding this result, Jermann and Quadrini (2012) point out that the procyclicality of equity issuance is not robust because its statistical significance varies depending on how equity issuances are measured. In this study, we examine cyclical patterns of debt and equity financing in Korean firms. Contrary to the results of Covas and Den Haan (2011), we find that the equity issuance of Korean firms is countercyclical. In a macroeconomic-level analysis using the flow of funds data from the Bank of Korea, the use of debt is positively correlated with the HP-filtered GDP of the previous quarter, whereas the use of equity is negatively correlated. In a firm-level analysis using the accounting data of individual firms, we find the same result-that debt financing is procyclical and equity financing is countercyclical. In particular, the countercyclicality of equity issuance has become stronger after share repurchases were permitted in 1994. This result stands in contrast to the case of U.S. firms, in which both debt and equity financings are procyclical. To explain why equity financing is countercyclical in Korea, contrary to the U.S. case, we extend the panel regression model used in Covas and Den Haan (2011) and explore how debt and equity financings, investments, and asset growths in corporations respond to the cyclical movements of the economy. Following Covas and Den Haan (2011), we allow coefficients to vary with firm size. We also use cash flows and Tobin's Q, respectively, as explanatory variables for current and future profitabilities. In addition, for the purpose of controlling collateral value, investment opportunity, non-interest tax-shields, and the effects of economic crises, respectively, we include tangible assets, intangible assets, depreciation, and time dummy variables for two economic crises. We find that the use of debt is procyclical for all firm groups and the use of equity is countercyclical for bigger firms. This result is consistent with that of the correlation analysis. While investments and asset growth are significantly procyclical for all firm groups, total assets vary more than investments as the business cycle changes. This implies that firms use financial assets as a buffer to insure against negative shocks during contractions. Interestingly, cyclical changes in debt are larger than those in total assets in Korea. This indicates that to finance the purchase of assets, Korean firms rely mostly on debt in boom periods, whereas they use equity only when it is difficult to raise debt in downturn periods. By contrast, U.S. firms utilize debt, equity, and retained earnings all the time to finance investment projects. The discrepancy between the two countries indicates that the cyclicality of corporations' financing behavior is determined not only by the substitutability of debt and equity, but also by such dynamic factors as the availability of internal funds and the difficulty of accessing the debt market.