The aim of the study is to examine the relationship between Wiki Collaborative Writing (WCW) and students' writing motivation. The first objective of the current study is to determine the relationship between WCW and self-efficacy, goal orientation writing, beliefs and affects about writing motivational components. The second objective of the study is to examine the effect of course specific and group specific motivational components on the changes of students' motivation levels. To achieve the first objective, quantitative data is collected through the implementation of a motivation test. Descriptive statistics and a Wilcoxon signed-rank test are used to analyze the data from the motivation test. To achieve the second objective, qualitative data is gathered through focus group interviews. Deductive content analysis is used to analyze the transcripts. The motivation test results indicate that there is a relationship between the WCW and the increase in student motivational levels with regard to self-efficacy, mastery goals, beliefs about writing content and beliefs' about "good writers do not make errors in grammar," and "writing quickly is an important part of good writing"—as well as students'' affects about "the writing process is satisfying," and "writing is interesting." There is a significance relationship between WCW and the reduction in students' motivation with relation to avoidance performance goals, students' belief that the main problem of poor writers is using incorrect grammar, the belief that revising is mostly about correcting grammar and spelling errors. However, there is no relationship between WCW and students' writing performance goals with regard to students' goals of completing all writing assignments and becoming better writers. The analysis of the interviews indicates that wikis' ease of use motivates students to access wiki pages regularly. Wikis' ease of use motivates students to organize and revise their writing. In addition, writing collaboratively through wikis reduces students' writing stress; wiki social features enhance students' writing motivation with regard to avoidance-performance goals. Moreover, the history function helps students evaluate their participation and writing abilities in comparison to their peers, which shapes students' writing motivation level with regard to revising and reflection strategies. Finally, being in a homogenous wiki group motivates students to be more interactive and collaborative.