提升企業資訊揭露的透明度，降低投資人資訊接觸的障礙，為政府推動公司治理改革的重要方針。證劵暨期貨發展基金會所推動的「資訊揭露評鑑系統」，正是希望以外部監督機制來促使受評公司之揭露政策能同時兼顧法規要求與資訊自願需求，俾能降低企業資訊不對稱的環境。緣此，本研究旨在探討年報中資訊揭露水準對資訊不對稱程度之影響。實證結果顯示，年報中所呈現的整體資訊揭露水準愈高，愈能有助於緩和企業資訊不對稱的程度。若進一步考量資訊揭露的性質，更可清楚發現自願性資訊揭露水準愈高，企業反應出的資訊不對稱程度愈輕，但此結論並不適用於家族控制企業及股份盈餘偏離程度高的企業，至於強制性資訊揭露降低資訊不對稱的效果則不明顯。本研究之政策意涵為：就降低資訊不對稱程度的立場而言，鼓勵督促企業提昇自願性資訊揭露的效果明顯優於以法令強制企業從事資訊之揭露。

To narrow the information gap between managers and investors, the Taiwan authorities have called for greater corporate transparency and treated itan important policy in the reform of corporate governance. In add as ition, the Taiwan Securities and Futures Institute has also launched the “Information Disclosure and Evaluation System” with the expectation that the outside monitoring mechanism can urge companies to strengthen their voluntary disclosure besides mandatory disclosure, and thereby reduce corporate information asymmetry. For the reasons given above, this study aims to examine the impact that the disclosure level of the annual report has on the degree of information asymmetry. The empirical results show that the disclosure level of the annual report is negatively associated with the degree of information asymmetry. If we further consider the nature of the disclosure, the evidence shows that the degree of information asymmetry will become lower as the level of voluntary disclosure becomes higher. However, this finding is not applicable to firms under family control or firms with a larger wedge between voting and cash flow rights. As for mandatory disclosure, its effect is not significant in reducing information asymmetry. The implication for policy is that the benefits from promoting voluntary disclosure are better than those from complying with mandatory disclosure regulations in terms of mitigating the degree of information asymmetry.