Depending on the improvements of information technology e-commerce and e-marketing have become very important concepts, making online shopping very popular. As a result of the proliferation of e-commerce and online shopping, "online impulse buying" has become an emerging phenomenon. Taking the lack of studies on online impulse buying into consideration this study is meant to contribute to this underdeveloped area. There are many factors effective on consumers' impulse buying. A variety of studies focus on these factors in traditional retailing but rare studies examine the factors effective on online impulse buying. These factors can be internal or external in nature. This study examines the effects of personality traits (internal factor) and web site quality (external factor) on online impulse buying. In the study survey instrument was used as the data collection method. Questionnaires consisting of the items of validated scales (e.g. Five Factor Model) on the related subjects were distributed. Results of the study will shed light on the design of the web-sites and will be helpful for all e-commerce firms that want to increase the level of impulse buying of their customers. (C) 2015 The Authors. Published by Elsevier Ltd.