2012 年 7 月 25 日，立法院三讀通過《所得稅法》修正草案，開啟了我國於 2013 年 1 月 1 日開徵、2016 年 1 月 1 日停徵之證券交易所得稅。我國證所稅曾歷經四次開徵，最後亦四次停徵。在這樣特殊的歷史下，為瞭解證所稅政策實際所帶來的效應，本文透過差異中的差異法 (difference in differences)，探討在證所稅實施期間，證所稅課徵實際對臺股交易量之影響。研究資料係以臺股 2012 年 7 月 1 日至 2015 年 12 月 31 日不同市場之成交金額為樣本，將「臺灣興櫃整體市場成交金額」作為實驗組，再以「上櫃市場外資成交金額」作為控制組，以差異中的差異法進行實證分析。實證結果顯示，於證所稅政策實施後，控制組「臺灣興櫃整體市場成交金額」減少約 9%，代表臺股交易量確實會受到證所稅之負面影響，呈現一定量的減幅。惟本文認為這樣的結果，亦顯示證所稅應不致於對臺股市場造成太嚴重的衝擊，反而可以讓當政者去思考，在縮短貧富差距及促進資本市場發展間，如何去取捨拿捏，以盡可能達成租稅正義的目標。

On July 25, 2012, the Legislative Yuan passed the draft amendment to the capital gains tax, which allows Taiwan to levy capital gains tax on securities transactions from January 1, 2013 to January 1, 2016. Taiwan has levied capital gains tax on securities transactions four times. However, the tax did not levy, eventually. In order to understand the actual impact of capital gains tax policy, this study employs the method of difference in differences to analyze the impact of the capital gains tax policy on the trading volume of Taiwan’s stock market during the implementation of the Act. Using the trading volume of Taiwan’s emerging stock market (Taiwan’s OTC Market) as the experimental group (control group), we find that the trading volume of Taiwan's emerging stock market has decreased by about 9% after the implementation of the policy. This indicates that the policy does have a negative impact on the trading volume, showing a certain amount of decline of Taiwan's stock market.

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