本研究旨在探討存在不同盈餘管理額型時，市場上所產生的反應，尤其是所得稅費用之盈餘管理意函。並探討實施兩稅合一後，對企業管理當局運用盈餘管理工具策略的影響及是否會改變投資人對企業的評價。
結果發現(1)不管是管理當局或者投資人都符合期望理論，對於達成盈餘目標者有較高的偏好與評價。因此，管理當局會運用盈餘管理工具達成盈餘目標，且短期內投資人也會對達成盈餘目標者有較高的評價。但就長期而言，投資人即發現採行盈餘管理的企業，盈餘缺乏持續性，而會給於較低的評價。(2)管理當局如果採用裁量性應計項目進行盈餘管理，投資者在短期內不容易察覺;若採用「所得稅費用」進行盈餘管理，則短期內即會被察覺而會給予較低的評價。(3)兩稅合一的實施後，投資者瞭解所得稅費用性質上的改變，但若與未達成目標者比較，企業運用所得稅費用進行盈餘管理，尚可得到短期的正向效果。

The purpose of this study is mainly to examine the market reaction of firm's earnings management activity by considering the discretionary accruals and the income tax， especially focusing on the later item. Because the tax rule of Taiwan was changed in 1998 so that the issue would be a good research topic for understanding whether the firm's management and investor perceive the change in expense property of income tax.
The results have shown: (1) both management and investor prefer the firm to beat marginally earnings target (avoid loss) in the short run， no matter how to reach the target. (2) Though the investor can't find that the firms use discretionary accruals to beat marginally earnings target in the short run， however， the investor will find easily the firms use income tax to beat the earnings target. In addition， in the long term， the investor will perceive the importance of earnings quality. (3) After implementing of the imputation tax credit system， the investor understands the change on the expenses nature of the income tax. The investor will give them a higher value about those firms use the income tax expenses to manage earnings to reach the target more than those who have not reached the target.