民國99年4月12日，國民黨立院黨團決議，支持營利事業所得稅（以下簡稱：營所稅）稅率全面由20% 再調降至17%，並配套將銜接「促進產業升級條例」之「產業創新條例」草案，其功能性租稅優惠縮減。本文對此一政府首度確定營所稅稅率將再次調降的消息，進行事件研究，探討該事件對上市公司股價異常報酬之影響。研究結果發現：（1）市場可能普遍預期稅率全面再降對企業有利，故股價產生顯著正向之異常報酬。（2）電子業與非電子業公司之異常報酬反應有顯著差異。投資人對稅率全面再降，視為是非電子業公司價值利多的好消息，使股價上漲而產生顯著正向之異常報酬；但對電子業公司則視為是價值利空的壞消息，使股價下跌而產生顯著負向之異常報酬。（3）在企業財務特徵上，大小企業規模、高低獲利能力不同之公司，其異常報酬亦存有顯著差異。獲利低、規模小的公司，為此次政府宣布企業全面再減稅的受惠者，故其股價上升，產生明顯的正向異常報酬。

On April 12, 2010, the Kuomintang legislative caucus resolved to support a further reduction to 17% from 20% in corporate income tax (hereafter referred to as income tax). This reduction in income tax was supported by the drafted "Industrial Innovation Act," which was designed to reduce functional tax incentives and, in function, followed the termination of "Enforcement Rules of the Statute for Upgrading Industries." This study investigates the effects of the news of a further income tax reduction for enterprises, which was announced on April 12, 2010. We apply event study to analyze the abnormal returns of the companies listed in the Taiwan Stock Exchange (TSE). The results showed that: (1) The stock market reacted significantly and positively to the announcement of a corporate tax rate reduction from 20% to 17%, suggesting the additional tax reduction was widely expected to benefit enterprises. (2) A significant difference exists between the abnormal returns of companies in the electronic and non-electronic industries. Investors regarded the additional tax reduction as good news for the non-electronic industry, increasing stock prices and significantly positive abnormal returns. By contrast, the tax reduction was regarded as bad news for companies in the electronic industry, resulting in a decline in stock prices and significantly negative abnormal returns. (3) Significant differences exist between the abnormal returns of companies with different corporate financial characteristics, such as firm size and profitability. Once again, small companies or companies with low profitability are the beneficiaries of the government's announcement to further reduce enterprise income tax, experiencing an increase in share prices and significantly positive abnormal returns.