Accounts for an important portion of total assets, equity financial instruments (EFA) are mainly held for strategic purposes in non-financial firms. The International Accounting Standards Board (IASB) replaced the International Accounting Standard (IAS) 39 Financial Instruments: Recognition and Measurement with International Financial Reporting Standard (IFRS) 9 Financial Instruments, incorporating changes to the classification and measurement of EFA, effective in Jan 2018. The major changes for EFA accounting from IAS 39 to IFRS 9 include the prohibition of recycling fair value gains or losses on EFA from other comprehensive income (OCI) to profit or loss when derecognition and mandatory fair value measurement for all EFA without cost option as allowed under IAS 39. In this paper, we investigate whether there is a cost for EFA accounting in ASX 500 firms and how IFRS 9 affects it by examining audit fee models with a difference-in-difference approach. We find that (1) audit fee is positively related to firms that have EFA, and the positive relationship is driven by large firms; (2) for firms that have EFA, auditors’ approach to corporate EFA fees has changed in the four years between the issuance and implementation of IFRS 9, from being based on EFA amount and level 3 fair value measurement for EFA after IFRS 9 early adoption to being based solely on level 3 fair value measurement for EFA independent of IFRS 9 adoption; (3) audit efficiency is not affected by EFA accounting regardless of IFRS 9 adoption. We expand audit fee literature and contribute to policymakers by shedding light on the association between audit fee and EFA and providing early evidence on the cost of implementing EFA accounting under IFRS 9.