Among various export contracts, the contents of contracts are very important. Various companies make use of this method. [Which method are you talking about?] However, the Korean law system has an insufficient understanding of the international legal system. This paper looks into the conditions related to contracts in relation to the legal system. This paper analyzes not only the Korean civil law system about illegality of contracts but also makes a comparison with other international systems, such as the UNIDROIT Principles. Especially, the Korean civil law system about the illegality of contracts is comparable with the UNIDROIT Principles system about illegality of contracts. The purpose of this paper is to examine the revitalization of Illegality of Contract. This paper also deals with improvement of International Commercial Activation. Thus, this paper will offer directions to International Trade Practitioners. There is disagreement regarding methods of action related to international trade practice. Especially, this study is good for commercial parties, especially overseas sales people.