In this paper, we have studied the impact of adopting XBRL (eXtensible Business Reporting Language) on information asymmetry in capital markets with the additional research on the usefulness of XBRL data how to improve the quality of accounting information. From the Kosdaq XBRL service, the samples are selected including 38 adopted companies and the 30 non-adopted companies for the paired analysis. The daily stock return volatility (VOLA) as independent variable and other several controlling variables have been added for the regression analysis to measure the impact on information asymmetry in capital markets. he analytical result indicated that the asymmetry hypotheses that XBRL data will give a significant impact on the capital market and will reduce the volatility, which are expected in the hypotheses. This is the first analytical research on the capital market and its impacts to the capital market from adopting XBRL based accounting information. Additionally, the analysis showed the impacts on the reporting cycle of accounting information and its usefulness of accounting data itself.