This paper examines whether or not XBRL (eXtensible Business Reporting Language) adoption reduces information asymmetry in a stock market context. Student t-tests and multiple regression analysis were employed to examine the effect of XBRL adoption on information asymmetry in the capital market. A significant and negative association exists between XBRL adoption and information asymmetry, which implies that the adoption of XBRL may lead to the reduction of the information asymmetry in the Korean stock market. In addition, the effect of XBRL adoption on reducing information asymmetry is stronger for large-sized companies than for medium-sized and small-sized companies. Based on these findings, the demand for XBRL-enabled applications and services in the capital market is expected to grow while governments should promote XBRL adoption for business reporting. (C) 2010 Elsevier Inc. All rights reserved.