許多研究指出開放外資投資國內股票市場的好處，但卻很少文獻探討外資是否有促進市場效率的功能。因此本研究旨在探討外資持股比例的高低是否會影響公司價格效率性。我們使用台灣證券交易所的資料，以2007至2016年間所有外資持股的台灣上市公司為樣本，進行分析。其中，我們使用日報酬的一階自我相關係數來衡量價格效率性，當係數趨近於零時，表示價格是有效率的且遵循隨機漫步。研究結果顯示，在台灣股票市場，無論是整體股票市場，或是分別以各產業及外資持股高低的四個組合來看，外資持股比例的增加並沒有助於公司價格效率性的提升。 / Various benefits of opening a market to foreign investors are indicated in prior studies. However, few studies point out whether foreign investors improve efficiency of stock prices. Using a large sample of TWSE-listed stocks over the period 2007 to 2016, we investigate the relation between foreign ownership and price efficiency. In our analysis, we use the first-order return autocorrelations, which should be zero if prices follow a random walk to compute price efficiency. After controlling for the change in foreign ownership, firm size, stock price and stock liquidity, finally, we find that stocks with greater foreign ownership are not priced efficiently whether in overall market or in each level of foreign ownership and also in different industries. In summary, these results suggest that the foreign investors could not improve price efficiency on the Taiwan stock market.