To examine the impact of women on boards (WOB) and of Japan's corporate governance (CG) code on earnings quality (EQ), we explore women's roles in enhancing EQ and their interactions with bank monitoring within a bank-based financial system. This report intends to reveal whether the role of WOB complements or substitutes for the monitoring of main banks to enhance EQ in Japan. Our study also focuses on Japan's dual audit system as a unique institutional setting. This report contributes to the discussion of whether the presence of WOB effectively enhances EQ in bank-based systems. This report will provide insight into the effectiveness of the CG code in promoting greater representation of WOB and contribute to “Who are effective monitors to enhance earnings quality”.