本研究係探討關係人交易雙方是否委任相同會計師進行查核，對企業負債資金成本之效果。本文以企業利息費用除以平均帶息負債衡量企業之負債資金成本，企業之關係人交易部分則分成關係人銷貨交易、關係人進貨交易、關係人應收款、關係人應付款等四類型交易，來討論關係人交易與企業負債資金成本之關聯，接著將各類型關係人交易再細分成由相同會計師查核關係人交易雙方與由不同會計師查核關係人交易雙方兩類，以檢驗相同會計師查核對於企業負債資金成本之影響。 研究結果發現關係人交易與企業負債資金成本之關聯並無統計上之顯著性。然將關係人交易進一步拆分為是否由相同會計師查核關係人交易雙方後，關係人進貨交易與關係人銷貨交易等兩類型交易若由相同會計師查核交易雙方，其相較於不同會計師查核能夠有效減緩企業負債資金成本增加之情形。 / This study examines the effect of same auditor auditing both sides of related party transactions (RPTs) on cost of debt. In this study, cost of debt is measured using interest expenses divided by average interest bearing debt and we hand collect from annual reports the data of the four common types of RPTs: sales to related parties, purchases from related parties, accounts receivable from related parties and accounts payable to related parties. For the four types, we further split RPTs into RPTs whose involved sides are audited by the same auditor and RPTs whose involved sides are audited by different auditors. We do not find any evidence that RPTs are associated with cost of debt. However, we find that for sales to related parties and purchases from related parties, RPTs whose involved sides are audited by the same auditor are associated with cost of debt less strongly than RPTs whose involved sides are audited by different auditors. Our results suggest that same auditor auditing can mitigated the detrimental effect of RPTs on cost of debt.