本文探討會計師事務所專業中一直較少被文獻討論，然而在實務經營卻極為重要的業務多樣化策略與其財務績效間之闗係。經以台灣財政部發行之1995-2002年的合夥型會計師事務所資料進行分析，主要結果有以下兩項。首先，會計師事務所之業務多樣化程度與其財務績效間，因為規模報酬狀況之差異，而呈非線性之倒U型關係，亦即會計師事務所處在規模報酬遞增 (減) 的狀態時，其業務多樣化程度愈高則呈現財務績效愈高 (低)。此一結果隱含業務多樣化程度有最適點之存在，專業服務業之實證結果亦類似於全球經濟體系中各產業之實證結果，即相關性業務多樣化程度與企業績效之非線性關係。其次，由於本文之實證樣本納入規模較小之合夥型會計師事務所，故實證結果自然地延伸了相關文獻指出業務多樣化愈均衡時，其財務績效愈高之理論預期，進一步發現到較小 (大) 規模會計師事務所，其業務多樣化程度較不均衡 (均衡)，且財務績效較差 (佳) 之不對稱的關係。前二者之實證結果可供會計師事務所之管理階層加以參考。 This article discusses the relationship between business diversification strategies and financial performance, which is rarely discusses in professional documents, but has been the most important component among actual practical managements in the partnership accounting firm area. The data of partnership accounting service firm from 1995 to 2002 had been analyzed by the Taiwan Ministry of Finance; there are approximately two main results from this analysis. First, due to the difference of the returns to scale condition, the relation between the diversification of accounting firms and its financial performance is shown as a non-linear, inverse U shape graph. When firms are under the condition of increasing (decreasing) returns to scale, the higher (lower) level of business diversification, the higher (lower) financial performance they will experience. This result indicates that there is a most suitable spot in business diversification; the result of specialized service industry is also similar to the experimental result of the global economic system in various industries, which shows a non-linear relation between service diversification and enterprise performance. Second, since the real diagnosis of this article integrates the sample of small partnership accounting firms, the result naturally extends the correlation and theory that financial performance will be higher when the business diversification is more balanced, which further discover that the smaller (bigger) scale of the accounting firms, their business diversification will be more imbalanced (balanced), that financial performance will reflect badly (better) as asymmetrical relations. The diagnosis results of the above may supply as references to the management class of accounting firms.