This paper investigates the relationship between the characteristics of the two-tier board structure (board of directors and supervisory board) and the disclosure of key audit matters (KAMs) in the expanded audit report. Using a sample of 10,857 firm-year observations of Chinese listed firms spanning the 2017-2020 period, we offer two main results. First, with regard to the board of directors, we find that the auditor discloses a greater number and lengthier content of KAMs when there is a CEO duality and the board meetings are more frequent. Second, conversely, we find that the size and independence of the supervisory board are related to a lower number and length of KAMs disclosure. When we distinguish between account-level KAMs and entity-level KAMs, our further analysis shows that our results are principally associated with account-level KAMs rather than entity-level KAMs. Specifically, we find that CEO duality and the frequency of board of directors meetings are positively related to account-level KAMs. We also find that the size and independence of the supervisory board are negatively related to account-level KAMs. Our further analysis also shows evidence that these two-tier board structure characteristics are associated with the tone of KAMs disclosure in a consistent fashion. Our findings are robust and address endogeneity problems. Overall, our results suggest that the characteristics of the two-tier board structure drive KAMs disclosure, which should be of interest to regulatory bodies, policymakers, auditors, multinational firms, and users of financial reports.