© 2015 Elsevier Ltd. This study examines the effect of eXtensible Business Reporting Language (XBRL) on audit fees, and assesses whether and how this effect varies across different countries. We specifically consider publicly listed firms in the US and Japan over the eight-year period centered around the dates on which XBRL was first mandated for use by publicly listed firms in these jurisdictions. Our comparative results show that XBRL use is inversely associated with audit fees, which are in turn positively associated with firm size. We also find that, overall, XBRL moderates the association between firm size and audit fees in both the US and Japan. However, these moderation effects are weaker among Japanese firms.