The purpose of this study id to examine the effect of Web site usability on the revisiting intention of customers in Internet book stores. The Web site usability construct consists of the factors such as contents, design, navigation, and interactivity. In order to accomplish the purpose of this study, a research model was established and it suggests that the usabililty effect the revisiting intention of online customers in Internet book stores. The results of the study show that contents, navigation, and interactivity has statistically significant effect on revisiting intention of Internet customers and this effect is mediated by perceived ease of use and perceived usefulness. This research confirms the importance of usability construct in designing web sites and understanding the use of web sites. Implications of these findings are discussed for researchers and practitioners.