企業的經營方式隨時代演變而改變。在全球化競爭與資訊科技迅速發展的時代，供應鏈競爭已成為新趨勢。相同供應鏈的公司之間往往具有商業互補性，所以容易形成聯盟或合作之關係。雖然提高公司之間的商業互補能開創公司的競爭優勢，卻可能惡化會計師的審計品質，降低公司財務報表的可信度。董事會的管理是公司治理的核心，健全的董事會是否能達成公司治理之目標，是值得關心的問題。本研究先測試在相同的供應鏈體系下，會計師查核的客戶數是否與其審計品質呈負向關係；再行探討董事會特性與審計品質間的關係；最後檢測監督性質較佳的董事會是否可以抑制商業互補對審計品質的影響。本研究發現，在相同的供應鏈體系下，會計師同時查核公司與其供應商，其審計品質低於只查核一家公司；換言之，會計師查核的客戶數與其審計品質負相關。此外，外部董事比率較低者、董事長未兼任總經理或董事會規模較大者為監督效果較佳之董事會，其有助於降低裁決性應計數絕對值，使會計師獨立性得以維持，提升審計品質。再者，監督性質較佳之董事會有助於抑制商業互補對審計品質的傷害，於受查公司與其供應商的樣本中獲得支持。 Companies will change their business models to fit their environment for survival and development. Competition among supply chains has become a new tend in cutthroat global competition and high-speed changing information technology environment. There is a relationship of business complementarity between companies if they are in the same supply chain. Therefore, they may easy to become alliances or cooperative partners. Increasing business complementarity between companies could create competitive advantage for a company, but it might deteriorate CPAs’ audit quality and reduce the reliability of corporate finance statement. How to manage the board of a company is the key point for corporate governance. It is an important issue if healthy board of directors can achieve the goal of corporate governance. In this paper, we test the association between CPAs’ client number and their audit quality in the same supply chain firstly. Then, we investigate the relationship between characteristics of board and audit quality. In the end, we examine whether good characteristics of boards of companies can reduce the effect of business complementarity to deteriorate CPAs’ audit quality. We find that CPA’s audit quality is higher significantly if CPA audited one company than audited both the audited company and its supplier. In other words, between CPAs’ client number and their audit quality has a negative relationship. Furthermore, the board which has lower outside director ratio, a board chairman doesn't pluralize CEO, and the board size is larger has better monitor effect, that can decrease the absolute discretionary accruals, maintain the CPA’s independence to increase audit quality. And a board which has better monitor effect could suppress the effect of business complementarity between companies on deteriorating CPAs’ audit quality.
