本文探討D&O保額適當性與審計公費之關聯性，研究結果顯示公司之正常投保金額越高，會計師所收取之審計公費越低；然而，當公司之異常投保金額越高時，會誘發公司內部的投機行為，因此會計師所收取之審計公費越高。進一步檢視具有保險業務關係之機構投資人與D&O保額之交互作用，發現當機構投資人具有保險業務關係時，會擁有較多之資訊優勢，可加強正常投保金額所帶來的監督效果，減少審計公費；但當公司投保過多的D&O保額時，具有保險業務關係之機構投資人因為利益衝突，害怕反對管理階層的決策會喪失現有或未來潛在之業務機會，反而無法制止異常投保金額可能引發的投機行為，因而提高審計公費。

This paper first examines the relationship between the appropriateness of D&O insurance coverage and audit fees. The results show that if the firm purchases appropriate (normal) D&O insurance coverage, as the normal D&O insurance coverage increases, the auditor charges lower audit fees. However, if the firm purchases excess (abnormal) D&O insurance coverage, it has an adverse effect on the directors' and managers' behavior and increases the litigation risk. Hence, as the abnormal D&O insurance coverage increases, the auditor charges higher audit fees. Further analysis examines the interaction effect between the D&O insurance coverage and institutional investors who have insurance business relationships with the D&O insured companies on audit fees. The examination reveals that when the firm purchases appropriate D&O insurance coverage, the institutional investor in the insurance business relationship has an information advantage, which enhances the monitoring mechanism. Thus, the auditor charges lower audit fees for the client who has an institutional investor in the insurance business relationship. On the other hand, when the firm purchases excess D&O insurance coverage, due to conflicts of interest, an institutional investor will be afraid of losing current or potential business if they oppose management's decisions. The institutional investor will be less likely to deter the directors' and managers' opportunistic behavior, which increases the firm's litigation risk. Thus, the auditor charges higher audit fees for the client who purchases abnormal D&O insurance coverage and has an institutional investor in the insurance business relationship.