A currency exchange system is introduced for a multi-currency electronic money trial, in which smartcardbased electronic moneys (two currencies) are circulated over the Internet. Considering the need to support our existing single currency electronic money protocol, the exchange method proposed herein offers fairness between untrusted parties based on the “optimistic approach”. This paper describes the concepts and basic specifications of the currency exchange system as well as evaluation results of the trial held from October 1999 to March 2000.