本研究探討會計師事務所合併事件期間，參與合併之會計師事務所客戶股份的反應。若審計品質會因合併而增加，則股東與公司經理人員間利益不一致之情形將因此減少；此外，會計師事務所合併將使股東於公司破產時，可自會計師處獲得之期望賠儐金額增加。因此，根據Wallace(1980)審計需求於獲悉會計師事務所合併之消息時，客戶股價應有正的異常報酬。本研究針對國內三次會計師事務所合併之事件期間有顯著的異常報酬。然而，正義食品案發生後，我國會計師須負擔之法律責任似有增加之趨勢，進一步的分析顯示，正義食品案發生後的兩次合併之事件期間的思積異常報酬高於該案發生前一次合併之事件期間的累積異常報酬，與保險假說之推論一致。

　　　　　The paper examines the audit clients' stock price reactions to the announcement of a CPA-firm merger. According to the agency hypothesis proposed by Wallace (1980), the inconsistence between shareholders' and the owner-manager's interests will decrease if the audit quality increases after a CPA-firm merger. While the insurance hypothesis indicates that the join up will raise the expected compensation to shareholders should the company go bankrupt. Therefore, the two hypotheses imply that, ceteris paribus, the stock price of the audit clients will have positive abnormal return when CPA firms announce their merger plan. In this paper, I focus on the data from three merger cases and use the modified event-study approach to empirically examine the market reaction to these mergers. Results show that there is no consistent evidence of considerable abnormal returns around the event date. However, it seems that the CPAs' legal liability has increased after the episode of Cheng I Food Company case. Further analysis shows that the cumulative abnormal returns of the CPA's clients for the tow mergers after the incidence are higher than those of the single merger before the incidence, which is consistent with the insurance hypothesis.