Two kinds of security devices such as independent guarantees and standby letters of credit have been widely used in the international transactions. These devices design to protect one of the parties from a breach by its counter-party. Main uses of these guarantees and standby letters of credit are as follows : bid guarantee, performance guarantee, advance payment guarantee, payment guarantee, retention guarantee, etc. The standby letters of credit were first invented in the U.S.A. and have been widely used in the international and domestic contracts in the U.S.A. But the practical use of these credits is very unsatisfactory in Korea. The purpose of this study is to serve the increase of practical use of the standby letters of credit in Korea through the comparison study on the practical use of the credits between Korea and the U.S.A. Both devices are very similar in function, but they are very different in forms. The one has the form of letter of credits but the other has the form of guarantee. The letter of credit has the stability of governing rule, the legal certainty, and the preference in the field of the trade community comparing to the guarantee. I recommend to use standby letter of credit instead of bank guarantee in international transactions because of the merits of the credit aforesaid.