We use the data of private enterprises, which consists of companies traded on the National Equities Exchange and Quotations in China from 2017 to 2024 and examine whether the voluntary establishment of an audit committee can enhance the audit quality. We find that the voluntary establishment of an audit committee can reduce the degree of accrual-based earnings management in private firms, which suggests that audit committees can indeed enhance audit quality, even in an environment characterised by both weak internal and external governance. Further results indicate that the role of audit committees in enhancing audit quality becomes more pronounced when both external and internal governance are weaker, suggesting that audit committees exert a meaningful governance effect in private firms. Our conclusions remain robust across a series of additional tests. We also find that the observed improvement in audit quality is not driven by auditor size or by higher inherent firm quality. Overall, our study enriches the literature on the governance effectiveness of audit committees and provides new empirical evidence on corporate governance in private firms.