This article explored the customers protection regulations in electronic payment system by Article 4A of the UCC and EFTA of 1978 and by Electronic Financial Transaction Act of Korea. Both Korea and America have various regulations to protect concerned parties(customers). For examples, the errors of payment order, money-back guarantee, and unauthorized payment order etc. First, this Article focuses on the allocation of risk of loss caused by ambiguous term in payment orders that do not express the subjective intention of the senders. Second, most rights and obligations created by Article 4A of America can be varied with the agreement of affected parties. But there are some exceptions. The exceptions include the money-back guarantee. So Receiving bank have to pay to originator the ordered money included interest. However, Korea also has money-back guarantee but bank do not pay interest to sender. Lastly, Electronic Funds Transfer Act of 1978 and Regulation E has US$ 50 regulation in order to protect customers on the unauthorized payment order. Article 4A imposes duty to detect unauthorized payment orders to originator in relation to the establishment of commercially reasonable security procedure, while Korean law imposes the duty to notify the bank in order to decrease the loss resulted from unauthorized payment order.