With the advent of new customs and practice of electronic records, the eUCP provides some useful guidance to accommodate the presentation of the paper documents electronically and also provides necessary rules to allow the UCP and eUCP to work together. There is no denying the fact that many of the UCP articles are not impacted by the presentation of electronic equivalent of paper documents, so the integrated application of the UCP and eUCP will be broad enough to allow for developing practice in this area. This study discusses some theoretical implication for efficient utilization of the global usages of letter of credit through the finding of optimal solution in the state of uncertainty caused by the electronic presentation of documents. This study suggest that the decision rules be developed to show how individuals choose optimal portfolio between the eUCP and the UCP that maximize their expected utility in letter of credit transaction, and also suggest that the optimal portfolio be determined at the point of tangency between the efficient trading line and the highest indifference curve in the mean-variance plane. This study finally recommends three rebuttable doctrines with regard to the relationship between the eUCP and UCP such as linkage characteristics, generation lap propensity, and homothetic application rule, which may be the critical standards for understanding of the integrated usages of the eUCP and UCP.