SUMMARY
This article aims to study the effect of Extensible Business Reporting Language (XBRL) on audit fee in listed companies in Tehran Stock Exchange (TSE). In this regard, we designed two hypotheses. The statistical population consisted of all listed companies in TSE. Data were collected using a desk study. The data were collected through sample company data by referring to the financial statements, explanatory notes, and TSE weekly and monthly reports. Simple and multiple linear regressions were employed for hypothesis testing by Eviews 7. The comparison of results indicates that XBRL is inversely related to audit fee which is positively correlated with firm size. XBRL is determined to be the mediator in firm size-audit fee relationship.