Although teacher reflection has been hailed as a crucial component that improves teaching and learning processes, the topic of factors affecting teachers’ reflective practices is yet to be thoroughly investigated in Vietnam. This qualitative study explores on-action reflective teaching among Vietnamese teachers, a critical aspect of professional teaching practices that remains understudied in the Vietnamese context. Grounded in the model of reflective practice and ecological systems theory, the study investigates the factors influencing reflective teaching practices of Vietnamese English as foreign language (EFL) teachers. Data were collected through semi-structured interviews with 15 EFL teachers working at different schooling levels. The findings reveal that reflective teaching practices are affected by numerous factors at multiple levels, including teachers’ beliefs and attitudes, cultural norms and societal expectations, institutional support, and student feedback.