This study relates to the toxicological clauses of the letter of credit. Some clauses which interferes with the recovery of the beneficiary in the letter of credit transaction, are called a malicious special condition or a toxic clause. The toxic clauses in a letter of credit transaction requires careful consideration because it may be impossible for the beneficiary to meet the document requirements, or it may be very difficult, even if it seems unlikely that the toxic clause is correct. We investigate the causes, types and prevention methods of toxic clauses which are abused in documentary credits, focusing on Korean and Chinese trade practices. First, the cause of the toxic clauses can be divided into the good toxic clauses and the bad toxic clauses, and in general, the toxic clauses means the latter. Second, the types of toxic clauses can be divided into explicit toxic clauses and implicit toxic clauses. Especially explicit toxic clauses are to restrict the entry into force of the letter of credit, to limit the signature of the quality inspector, to limit the shipment, and related to shipping documents etc. The practical considerations of the toxic clauses in documentary credit are that dealt with the choice of the trading partner, the choice of the bank, and the use of the trade contract. In particular, careful attention is required if the “APPLICANT”, who is not a direct party to the documentary credit, appears under special conditions in SWIFT 46A and 47B.