The present study addresses the question of how to support the professional development of English teachers with no subject-specific training apart from the formal channel of pursuing a Diploma of Education. This paper aims at finding out whether it is possible to employ action research as a means of professional development. It reports the cases of how three primary school English teachers with no subject-specific training grow professionally and change their methodology in teaching English through action research. Qualitative research method is adopted. Pre-interviews and post-interviews conducted by the researcher with the teachers and the students, journals written by the teachers, class observation reports written by the researcher, and post-lesson observation conferences between the researcher and the teachers are used to collect data. Triangulation is employed in data analysis. The findings suggest that action research can be an effective means to help non-subject trained teachers improve English teaching. This provides an option for professional development of language teachers.