Rapidly developing web technologies have increased the prevalence of user-generated Internet content. Of the many websites with user-generated content on the Internet, one of the most renowned is Wikipedia, which is the largest multilingual free-content encyclopedia written by users collaboratively. Nevertheless, although contributing to Wikipedia takes time and knowledge, contributors are rarely compensated. As a result, there is a need to understand why individuals share their knowledge in Wikipedia. The aim of this study was to evaluate the effects of both conventional and self concept-based motivation on individual willingness to share knowledge in Wikipedia. After performing an online questionnaire survey, SEM was applied to assess the proposed model and hypotheses. The analytical results showed that internal self-concept motivation is the key motivation for knowledge sharing on Wikipedia.