This study aims to explore changes in motivation that English teacher-researchers have towards teaching and research and the factors that prompted the changes. Ten in-service elementary English teachers participated in the study. Of the ten participants, four were doctoral candidates enrolled in an English teacher education course, and the remaining six were master’s students in a thesis-advising seminar. Surveys, journals, interviews, and final papers or master’s theses were collected. The data were qualitatively analyzed. Four patterns were found in regards to the participants’ level of motivation towards teaching and research: continuous low motivations, dynamic changes in motivations, highly maintained motivations with close relationships with participating students and teachers, and continuous high motivations to conduct action research. The factors that prompted the teacher-researchers’ changes in motivation were (a) intrinsic motivation related to teacher-researchers’ responsibilities for teaching and research as well as willingness to develop professionally, (b) research and teaching process and context, (c) interactions with colleagues in the research community provided by the teacher education program, (d) students’ reactions and feedback, (e) becoming an English subject teacher, and (f) multi-tasking in school work and individual factors. The results indicate the importance of improving English teacher-researchers’ motivations for their professional development. Further important implications regarding teacher-researchers’ development were discussed.