本研究探討不同規模會計師事務所合併對其受查核客戶財務報表價值攸關性之影響，推論會計師事務所合併會增加審計品質，進而影響受查核客戶財務報表價值攸關性。會計師事務所合併採用勤業與眾信及致遠與榮聰兩件不同規模合併案，並以台灣上市上櫃企業為研究對象。研究發現，合併前之勤業與合併前之眾信在受查客戶價值攸關性沒有顯著差異，符合認為此兩間大型會計師事務所因規模相當而在受查客戶價值攸關性沒有顯著差異之影響；合併前之致遠與合併前之榮聰在受查客戶價值攸關性也沒有顯著關係，其不符合規模較大會計師事務所受查客戶價值攸關性較小型高之預期。接著會計師事務所合併後，發現勤業眾信受查客戶在損益表價值攸關性有顯著增加；而致遠榮聰受查客戶在財務狀況表之價值攸關性有顯著增加，兩者都符合會計師事務所合併後，其受查客戶價值攸關性提昇之結果。 This study discusses how the merger of CPA firms affects the value-relevance of audited financial statements. We hypothesized that the merging of CPA firms improves audit quality, which in turn enhances the value-relevance of audited financial statements. We studied the mergers of Arthur Anderson and Deloitte Touche Tohmatsu., CPAs, and Diwan, Ernst & Young and J.T. Lai & CO., CPAs, using listed firms in Taiwan as research subjects. Results showed that the value-relevance of clients audited by Arthur Anderson and Deloitte Touche Tohmatsu showed no significant difference before the merger. This is line with our expectation that because these two large firms were relatively similar in scale, the value-relevance of the clients they audited was not significantly different. The value-relevance of clients audited by Diwan, Ernst & Young and J.T. Lai & CO. also showed no significant difference before the merger. This is not in line with our expectation that clients audited by large firms have higher value-relevance compared to those audited by small firms. After the merger of Arthur Anderson and Deloitte Touche Tohmatsu, we found that the value relevance of audited profit and loss statements significantly increased. Likewise, following the merger of Diwan, Ernst & Young and J.T. Lai & CO, balance sheets audited for their clients showed significantly greater value relevance. These findings confirm our theory that the merging of CPA firms leads to enhanced value-relevance for audit clients.