The purpose of this study was to investigate what factors affect students' adaptation and continued use of a Wiki system for collaborative writing tasks through an extension of the Unified Theory of Acceptance and Use of Technology (UTAUT). This study was conducted in a general education course in a university in northern Taiwan. Data were collected from surveys of 103 students after their continued writing on the CourseWiki system for one semester. With structural equation model (SEM) analysis, results from this study partially confirm that, in the UTAUT model, factors of social influence have direct and significant effects on students' actual usage of the Wiki system. Moreover, students' actual use of the Wiki influences their intention of future use. This study successfully applies the extended UTAUT model and tests the predictive power in determining students' acceptance of a Wiki system in terms of their actual use and their behavioural intentions of future use. It further provides suggestions for future research and practice, and should contribute to theoretical understanding as well as practical application of learning technology in post-secondary teaching.