This paper aims at assessing reasonableness for restraining the independence principle in the operation of documentary credit in case of the illegality appeared in the underlying transactions. It has been a major rule under the independence principle to keep the credit operation free from the defences made by the issuing bank and/or credit applicant with a view to prevent the payment as specified under the credit. And also, it is generally accepted in the international commercial community to examine a presentation to determine, on the basis of the document alone, whether or not the documents appear on their face to constitute a complying presentation. Even though these two essences are major rules in the credit operation, if a presentation is made with the documents forged or materially fraudulent, the issuing bank can refuse to pay the documents in respect of fraud rule based on fraud exception for which a court of appropriate jurisdiction would enjoin such honour. Now we have newly come to another situation to determine whether or not we have to apply the same as fraud rule which is applicable to the illegality in the underlying contract under the new conception of illegality principle based on illegality exception. English Commercial Court handled the illegality case under the case of Mahonia Ltd., v. JP Morgan Chase Bank in 2003 and Justice Colman decided that issuing bank can rely on illegality affecting a letter of credit as an excuse for failure to pay. This judgement brought about the acceptance of illegality principle based on illegality exception as a defence to payment under a letter of credit as far as the illegality concerned in the underlying transactions. It is noticeable that this case will affect our international commercial community more to rely on the illegality in the underlying transactions as a good issue to stop payment for the issuing bank in the L/C operation.