In December 1999, the AICPA introduced WebTrust, a electronic commerce assurance service of ensuring safe trading on the web, in order to effect consumer confidence into electronic commerce. Shortly afterwards, CPA associations of other advanced nations, such as Canada, Australia, also adopted this service. This study focuses on introduction of electronic commerce assurance service of ensuring safe trading on the web. WebTrust assurance service expected to be the international standard in electronic commerce in the near future and not only as a source of income for domestic accounting firms, which have simpler income structure than the international counterparts, but also as catalyst for stimulating electronic commerce. The findings of the study are expected to contribute to accounting practice, academy of accounting and electronic commerce firms in the following ways. Domestically, as Korea is considering using the electronic commerce assurance service, this study will help promote adoption of WebTrust assurance service. This study has shown, in the midst of declining income of accounting firms by audit, a way to increase their audit boundary.