Despite the fact that Documentary Letters of Credit are involved in process of International Trade for many centuries, but their legal personality is very new and their life span is much shorter than their existence. In the middle of Eightieth Century, Lord Mansfield introduced legal aspects of LC operation for the first time to the Common Law System. Later, International Chamber of Commerce started to codified regulations regarding international operation of Documentary Letters of Credit in 1933 under the title of Uniform Customs and Practices for Documentary Letters of Credit and updated them constantly up to current date. However, many aspects of LC operation including fraud are not codified under the UCP which subjects them to national laws. Diversified nature of National Laws in different countries can be source of confusion and problem for many businessmen active in international operation of Documentary Letters of Credit. Such differences are more problematic in Common Law countries as a result of following precedent. For Example, legal aspects of International LC transactions under British Law are only based on case law, however, American Law addresses Letter of Credit Operation under Article 5 of Unified Commercial Code. Due to important role of English and American law in practice of international trade, current paper will try to compare their approach to autonomy principle of in LC operation, fraud rule as a recognized exception to it and search for answer to following questions what is definition of fraud, and what are standards of proof for fraud in LC operation, under English and American law?