內部稽核係內部控制之ㄧ環，其重要性在有系統地評估及改善公司的風險管理、控制及 公司治理之效能以協助組織達成其目標。發揮效能的內部稽核可以協助降低代理成本 （DeFond 1992; Anderson, Francis and Stokes 1993），本研究探討內部稽核功能對股權結 構與代理成本關聯性之影響。從代理理論觀點分析股權結構與代理成本關係之文獻發 現，經理人持股與代理成本呈負向關係（Ang, Cole and Lin 2000）。本研究參考Ang et al. (2000)以超額營業費用率及資產週轉率為衡量代理成本之代理變數，並基於內部稽核為 有助於降低代理成本的監督機制，納入內部稽核變數（內部稽核規模與內部稽核人員素 質），分析股權結構與代理成本之關係是否受到內部稽核的影響，以瞭解內部稽核在保 障組織資產安全與提升組織營運效率內部控制目標之效能。本研究預期，在控制經理人 持股及其他變數下，內部稽核規模及內部稽核人員素質與代理成本呈負向關係。 Internal Audit renders its importance by helping an organization accomplish its objectives via bringing a systematic, disciplined approach to evaluate and improve the effectiveness of risk management, control, and governance processes. An effective internal audit function helps reduce the agency costs. This research examines the relationship between internal audit function and agency costs. Ang, Cole and Lin (2000) found that ownership structure is related to the agency costs. Higher the shares owned by the managers, lower the agency costs. In reference to Ang et al. (2000), this research develops excess operating expense ratio and asset turnover ratio as measures for the agency costs. Due to the potential influence of ownership structure on both agency costs and internal audit function, this research uses the number of internal auditor and the quality of internal auditors as measures for internal audit function, and investigates the effect of internal audit function on the agency costs. The findings of this research will enhance our understanding on the effectiveness of internal audit function measured in terms of assets protection, avoidance of resources wastes and improvement of operation efficiency. We expected that higher the number of internal auditor and better the quality of internal auditor, lower the agency costs.