This study was designed to extend our knowledge of the differences between EFL teachers' beliefs of effective instruction and their actual classroom practices under the influence of different factors in the Vietnamese context. The paper took a qualitative approach using focus group discussion, journaling, non-participant observation and post-observation individual interviews as data gathering tools. Findings from this study indicate a wide gap that existed between what was believed and what was actually implemented by experienced teachers. Participating teachers valued and were actually aware of the benefits of interactive activities to students' communication skills. However, they adopted teacher-centred, GTM-oriented instruction in the classroom. The study teachers' perceptions of students' factors, traditional educational values and norms, physical working constraints, family roles and emotion appeared to affect their teaching practices in the classroom. This research has the potential to inform teacher development in Vietnam and in similar settings with the view to improving the quality of English teaching and learning.