EDI is one of the most important information technologies in todays business environment. This study is an exploratory study on the EDI control of Korean companies in their early stage of EDI implementation. The purpose of this study is to examine the impact of EDI controls on the security and usefulness of EDI systems for Korean companies who have adopted EDI. The data of fifty-one Korean companies for financial, manufacturing, and trade industries are collected by the mail survey and interview methods. The level of EDI control is mediocre on the average. The level of EDI security is low while that of EDI usefulness is mediocre. The empirical results show that the EDI controls in general improve the EDI security and usefulness significantly. Especially, the application and security control affect the EDI security significantly while the management, application, and security controls affect the EDI usefulness significantly. The gap between the level and perceived importance of control does not affect the EDI security but decreses the EDI usefulness at the marginal level of significance. The limitation of this study is that only a small number of companies are available for data collection because Korea is in the early stage of EDI implementation.