本研究旨在檢視不同規模型態的會計師事務所合併案對原受查客戶的經濟影響。透過觀察不同合併目的的大型事務所合併案(安侯建業合併與勤業眾信合併)、中型事務所併入大型事務所的合併案(榮聰併入致遠)以及中型事務所合併為大型事務所的國富浩華合併案(第一、敬業與建興合併為第六大會計師事務所)，檢視不同規模型態的會計師事務所合併後，其受查客戶的盈餘品質與市場價值是否較合併前整體提升? 實證結果顯示: (一)大型事務所間的合併，係有助於提升其受查客戶之盈餘品質，惟安侯建業並未提升其受查客戶之市場價值。而因受國際加盟所促成的合併–勤業眾信在合併後，有助於提升客戶的盈餘品質及市場價值。(二)中型併入大型事務所的合併案，並未提升受查客戶之盈餘品質及市場價值；但在事件日前後，市場投資人正面看待中型事務所「榮聰」的客戶轉由大型事務所「致遠」查核的價值。(三)中型事務所間的合併案，整體上能提升受查客戶的盈餘品質，惟實證結果未呈顯著，但市場投資人樂觀看待其客戶之價值。本研究的實證結果能增補審計文獻在探討會計師事務所合併是裨益於受查客戶上的研究闕口，供管制者、投資人與各界參考。 The purpose of this study is to examine the economic impact of the merger of audit firms of different types on the original clients. By observing the merger of large audit firms with different purposes of consolidation (the merger of KPMG and the merger of Deloitte), the merger of large audit firm with medium-sized audit firm (the merger of Ernst & Young) and medium-sized firms merged and became large firms (the merger of Crowe Horwath). Viewing whether the client''s earnings quality and market value were in excess of the overall growth after the mergers of audit firms of different types. First, the merge of large audit firms will help to enhance the earnings quality of their customers,but KPMG didn''t raised the market value of its customers.In addition,due to the international affiliate to the merger - Deloitte after the merger has significantly improved the customer''s earnings quality, and overall, its help to enhance the market value of its customers. Second, The medium-sized audit firms merged into large audit firms didn’t improved the earnings quality of the customers'' and the market value. Third, the merger of the medium-sized audit firms into the sixth largest audit firm has improved the profitability of the customers,but the empirical results are not significant. Futher, the market investors are optimistic about the value of their customers. The empirical results of this project aims to the field help gain more understanding of whether audit firm mergers benefit to the market value of the clients for regulators, investors and the community reference.