This study explores the effect of naked day trade on the volume and margin day trade. On January 2014, the competent authority allows investors to conduct naked day trade, which can buy and sell shares that did not own the same day. The sample period is from January 2013 to December 2014. The empirical results show that the total trading volume does not increase significantly in the post period. Meanwhile, the volume of margin day trade significantly decreases after the introduction of the naked day trade, suggesting that the naked day trade is a substitute for margin day trade. Individual investors who used the margin day trade before has turned to employ the naked day trades. Transaction cost is an important determinant.